Interviews are definitely tiring, especially if they are all day long events. I thought zoom interviews would be awkward but it’s really not bad! I’ve had a positive experience so far.
Just make sure you know why you want a PhD (if that is the type of program you are applying for). Know your career goals. I often was asked why I wanted to attend that particular program. Also, be able to describe your research interests, at least in a general way. If you know who you’re interviewing with, try to look at at least the abstracts of their recent papers so you can bring up some talking points! Good luck, you’re gonna be great