So here's one poll that was done after the debate:
Debate-watchers say Biden won first debate, but most felt "annoyed" — CBS News poll This is a YouGov poll of likely voters, fwiw. Appears to be demographically and ideologically representative too.
Actually, only 48% said Biden won, compared to 41% for Trump. Which makes me think that people who already support Trump say he won and people who already support Biden say he won. 48% and 41% are pretty close to
the current RCP average of national polls. (49.7% to 43.1%)
I've heard that political scientists think that the debates don't actually matter, and this poll would seem to be consistent with that. Voters who support Trump will (almost always) answer that he won the debate, and the same for those who support Biden.
There's 2 more debates to come, as well as one debate between the veeps. I don't expect any big swings in the polls to come from them.