Hey,
This sounds like a little bit of a tough situation, but as someone who had to apply to uni in Covd times, I didn't have any open days or applicant days in person (except for 1 super socially distanced applicant day for a uni I didn't even like 💀) so it's not the end of the world if you don't go to them all.
Seeing as you're yet to choose unis and apply, I'd suggest you decide on a few unis that you'll extensively reserach online and then based off that you choose 3-5 potentials and go visit them. If it helps, you could pick some unis next to each other (like 1 hour away neighbouring cities) and visit them on the same day.
If you've got no friends then you should definitely ask some siblings or cousins if you've got any/ are close to, to visit the unis with you.
You should definitely visit at least 2 of the unis in person because you need to understand how to travel home and there for holidays, emergencies etc. And you have to understand where the accommodation is in relation to campus, and where the amenities of the city are.
You should talk to a tutor at school about this, cos as far as I'm aware, my school had an 'open evening' (albeit virtual) for parents, teachers and students to discuss uni
Good luck!