Tetr.io is great — it does have ads (unless you have Adblock) but not impactful during gameplay at all and is usually the go-to for multiplayer games. Another normal Tetris game that’s more single-player oriented is jstris.
Sure, my 2020 Intel Macbook Air is a bit pokey compared to the newest models, but shouldn't a 3 year old computer be more than enough to play 40 year old game?