A PI gave me 2 days to accept his offer after I mentioned I still have another interview. Is this normal?
This means one of two things:
The PI has a certain set of needs right now and wants them met. Your needs are irrelevant. This will be the case for the duration of your employment - they'll be a decent boss until they need something and then that thing will be more important than anything you've got going on. This is a reasonably common PI mindset and most of them will respond to pushback - if you're assertive and can manage their expectations and needs this could be an ok fit for you.
The PI is cynically abusive to staff. This is a test. They want anyone assertive to get filtered out at this stage, because you'd just quit later in the face of abuse anyway. This is a shibboleth to identify postdocs who can be used and discarded. There is no way to make this job work for you. This PI is rarer but tends to be hiring a lot (for obvious reasons) and so you'll see them more than you would expect on the job market.
It's better to not work for either kind of PI if you can avoid it.
In negotiation theory, such a tactic is known as an exploding offer, and its adverse effects are well-known: rushing people into hasty decisions and giving them the feeling that they're disposable can create distrust and a flawed work relationship. It also signals desperation, which will damage the PI's brand if the word gets around.
Such offers can happen, but they are definitely not the norm, and could be interpreted as a red flag. Proceed with caution.
I think that the PI is pressing you improperly. I'd suggest replying that you need to have the details in writing before you can formally accept an offer. You can say that you are interested and "inclined to accept" but without making a definite decision prior to having the actual details.
This is likely to give you the time you need for the other interview. And if it isn't acceptable to the PI, then I'd worry whether everything is proper or not on their end.