M3 isn't even published anymore in the US (it did not include bonds though).
As Alex noted, the LCR is entirely unaffected if the FED purchases government bonds because both are level 1. See for example this BIS paper on P.58 for a simple example demonstrating this.
the Fed cannot control the federal funds
rate through routine changes in the quantity of reserves, also known
as open market operations (OMO)
as copy pasted from this FED note about the ample reserves regime. This is a direct effect of the ample reserves regime, where the reserve requirement ratio is zero.
Generally, OMO can mean a lot of things (purchase of all sorts of securities) but (ignoring the title), I think the main argument is about the purchase of government bonds? For short, this does neither affect the interest rate (in an ample reserves regime), nor the liquidity ratio (LCR) / capital requirement of a bank. The latter statement requires that the central bank is purchasing a highly liquid (level 1) asset though (which US government bonds are).
Insofar, as written in your post, a purchase of government bonds by the FED has
no direct impact on credit creation,
at least not via the LCR or interest rate channel. I am inclined to believe that this was the argument made by whoever you heard this from. I am less convinced they mentioned money supply because traditionally the monetary base is defined as currency in circulation plus reserve balances and while there are more liquid types, none include bonds in the US in any case (there used to be M4 and L which included T-bills but these were stopped long ago).
Lastly, the implementation of monetary policy has evolved considerably and repeatedly since the financial crisis. The FED also does not (anymore) target monetary aggregates when conducting monetary policy. I believe reading this answer might be interesting, although many others have different opinions about this subject.
Commercial bank credit is NOT part of M1. When a bank provides a loan, the borrower receives a deposit. From the perspective of commercial banks balance sheets, this increases credits on the assets side and customer deposits on the liabilities side. Most of the times (with mortgages it is frequently directly sent to seller of the house / or mortgage notary's account) this deposit is withdrawn quickly and usually sent to another bank (unless the seller's bank account is at the same bank as the buyer's). Therefore, an individual commercial bank cannot generate lasting increases in its deposits by granting loans.
However, the banking system as a whole does see an increase in deposits (thus money supply) despite constant amounts of central bank money. Leaving potential reserve requirements aside, the bank will still have risk/return considerations to take into account when providing loans. From an asset liability management perspective, loans are long-term claims on the assets side, while sight deposits are typically liquid and short-term liabilities. In essence, that is one of the main reasons justifying commercial banking - it's an intermediary that brings together investors and savers despite their diverging requirements. Banks can offer this service because they can diversify the credit and liquidity risks better than individuals.
For risk management, banks need to consider factors such as current and future
interest rate on loans and deposits, the likelihood of deposit withdrawals and credit defaults and the like. On top of this, banks are tightly regulated. Banks need to follow the standards of Basel III, which consist of 3 Pillars
Long story short, banks cannot simply give away loans without end. Also, credit creation by banks relies on a lot more details than the traditional reserve requirement (money multiplier) argument suggests. Specifically, it is not just the consideration of outflows (of deposits) and inflows being spread over time and normally only being a fraction of total deposits (which is where the name fractional reserve banking originated, as only a fraction of customer deposits have to be covered all the time). Since deposits created by the banking
system belong to the banks’ customers, the main driving force behind credit creation are customers, not banks themselves.
In fact, the FED does not even aim to affect the broad money supply. St.Louis FED research claims it's best to forget what we learnt about money aggregates in undergrad Econ. The so called dual-mandate aims to (somewhat interestingly) promote three (not two) goals: maximum employment, stable prices, and moderate long-term interest rates
Neither of these goals mentions money supply. Also, New York FED -
Money Supply states that
In 2000, when the Humphrey-Hawkins legislation requiring the Fed to
set target ranges for money supply growth expired, the Fed announced
that it was no longer setting such targets, because money supply
growth does not provide a useful benchmark for the conduct of monetary policy.
and FED - what is money supply claims that
Over recent decades, however, the relationships between various
measures of the money supply and variables such as GDP growth and
inflation in the United States have been quite unstable. As a result,
the importance of the money supply as a guide for the conduct of
monetary policy in the United States has diminished over time
This answer has a few charts illustrating that total money supply is not really directly impacted by monetary policy. For example, normalizing each series to Dec 2005 = 100 (monetary base - BOGMBASE, M1 - be careful, the definition changed in May 2020 if you look at the data on FRED, M2), the data looks like this (the code to replicate this is in the link: QE stands for quantitative easing)
The dual-mandate got its name from employment and the price level, because under full employment (not no unemployment), and stable prices, interest rates settle at moderate levels. For details, you can read Frederic S. Mishkin (2007) speech at Bridgewater College.
To summarize, the main goals of the FED are to keep prices stable and to promote full employment (closely related to a healthy economy / GDP). However, as just seen, there is only a weak relationship between measures of the money supply and GDP growth and inflation. Therefore, the central bank focuses on interest rates, not only the FED Funds market, but also longer term interest rates. Changing interest rates has a direct impact on demand for credit (by customers) and the risk metrics of banks (current and future interest rate on loans and deposits, the likelihood of deposit withdrawals and credit defaults, Basel III calculations, ...).
As written above, monetary policy has evolved considerably. For example, in the EUR area, so called Targeted longer-term refinancing operations (TLTROs) aim to offer commercial banks attractive long-term funding conditions. To stimulate lending to the real economy, the interest rate is negative and in a nutshell, the more loans participating banks issue to non-financial corporations and households (except loans to households for house purchases), the more attractive (the more negative) the interest rate. While ultimately there needs to be demand from customers, these favourable funding conditions make it easier (cheaper) to offer loans.