This might seem controversial, but you can play chess, either lichess (open source) or chess.com (more popular).
I am not a browser gamer, but i played bonk.io for some time. Its a fun pvp platformer.
Additionally, you can also look for multiplayer indie games on itch. It does not have a lot of multiplayer browser games, but if the laptop is “really trashy”, then running games natively should be faster than running them in browser.
It would be fine if such companies could simply allow to use vpn to bypass regional restrictions. Instead they specifically verify the country where the account is created.