Chess.com and Lichess are both popular online chess platforms, but they cater to different needs and preferences. Chess.com is a commercial site with a large player base and a wide range of features, some of which require a paid subscription. Lichess.org is a free, open-source platform that offers a comprehensive set of features without any cost.
But I like lichess😀
Tl;dr
Lichess for playing chess. Chess.com for social
Long answer
Take what I have said about Lichess with a grain of salt. I don't have a Lichess account but guessing from what i have played as a guest on Lichess I think it is better for games or free users. But on the other hand, Chess.com is better for socializing because of the larger playerbase and the various options to interact with other people like forums, clubs, and event/collabs. While chess.com is a free website, you have to pay for some features.
Chess.com also has variants (a point which I forgot to add that some people pointed out) such as 4-player chess, Bughouse, And Crazyhouse. I also find Chess.com has a better rating system than Lichess. When I play on Chess.com my computer which is kinda old ( from 2018 ) sounds like a jet engine. But when I play on Lichess I have no such issue. I am not going to talk about the UI or the pieces Because different people like different stuff. Note that I personally prefer Chess.com because a lot of my friends are here and I like the UI of Chess.com better.