Dems controlled both houses of congress. What stopped him from pushing his public option plan then?

Manchin and Sinema, mainly, but also the 60-vote filibuster threshold. Forgot already?

then why are people worried about project 2025 and “dictator on day 1” Trump?

Because reasonable people don’t want the president to attempt authoritarian rule in order to progress his agenda. The fact that it is possible to do that is a big fucking issue and yet here we are, watching it happen with Trump. That doesn’t mean Biden should do it. It should not [and cannot be allowed to] happen at all.