It's already been established that it's definitely possible, but we haven't had any vote audits, so if it did happen, we wouldn't necessarily even know. Alao, with all the crap that Elon was pulling in the last election, I find it really difficult to believe that there was no manipulation, and at this point going forward, it's out in the open entirely.
We have cases of Republicans stealing voting machine, hard drives prior to the presidential election too.
https://electiontruthalliance.org/ has enough convincing content for me.
Am I cynical? Sure, but the nationwide and widespread efforts at voter disenfranchisement are enough for me to be satisfied that my doubt is valid. If this is what they're doing right in front of their faces, then why wouldn't they also be taking actions that we don't know about?