I’ve played through on the original classic server (before it went to BC and onwards). It’s fun, and full of nostalgia, but you have likely forgotten the endless grind to get enough gold to buy your skills, to buy a mount, to get even functional gear, and that outside a handful of classes, how difficult it is to do on your own. It’s endless, even if there was a small guild to help.
I am still a current player in WoW (retail), and if you need help, I can absolutely help spot bags, cash, and carries if needed, but I stopped with the Classic servers because of all the work. And the people there run from “old fogies” like me that played since Vanilla was live and are generally helpful, to people who pop in from retail and try to play the game that way.
For the record, the last two expansions (Dragonflight and now World Within) are a lot better, and some things have finally made in back into the game like useful talent trees. I have a current but very quiet thread for them.
Anyway, if you pop into retail, most of my active characters are on Wyrmrest Accord, which has plenty of active population. If you go classic, as suggested upthread, check the server population, and be prepared for a LOT of hours of grinding. Best of luck!