Many of them probably do, but I strongly doubt they're doing a ton of trading after hours. For one thing, the people all excited about gamestop have been talking about it at $40-50 / share, so why would they suddenly all jump in at $150? For another, I read (but don't know how to verify) that after-hours volume was much higher. Doesn't seem likely that retail was much of a factor.

Robinhood only allows you to trade for an hour into after hours. WeBull, another retail platform, and I believe thinkorswim (TDA's offering) allows you to trade the full after hours length of time which ends at 8pm EST.

edit: These are the only 3 platforms I have experience with, there are certainly others.

"reddit" being the chatty ones on wsb. Certainly don't claim it from what they write

Of course it could be that nobody posting on reddit has a single share, and all the screenshots are just virtual profiles on various accounts, but if we're assuming what people on reddit are saying is broadly true then that's the case

Ameritrade does. Not sure about RH.