I scoured the web and couldn't find an answer:
Does M1 Finance support specific identification of tax lots?
With Vanguard, when I go to sell, it gives me a list of tax lots and I just check the ones I want to sell (in full or in part). I assumed that this would be trivially easy at all normal brokerages, but, not only is that not the case, M1 Finance doesn't really give you a normal brokerage account in the first place.
Unless someone else has experience otherwise, I'm going to assume M1 Finance doesn't support anything other than average cost, single category.
For context: I know it's a bit more work to use specific identification, but it's saved me a good chunk on taxes by letting me take losses pre-FIRE and defer the gains until post-FIRE when I'm in the 0% long-term capital gains bracket.