I plan to update this version for a while
The most central problem for me personally is that the Steam client has been a literal health hazard since 2019. If I buy a game there, I don't get access to the game. The over $3000 worth of games I bought there before 2019 have been effectively stolen from me by Valve because of the problem, and their refusal (not failure) to fix it.
They've directly acknowledged that they're not just aware of the problem, but were made aware of it within a few days of the update which caused it. Their response started out with a direct promise not to bother taking appropriate steps to fix it, and has only escalate to more abusive behaviour since. That includes violating privacy rights of affected (former) customers, trying to gaslight people, and in at least 2 instances I'm aware of, trying to coerce people into self-harm.
There's a bunch of reasons other people dislike them as well, with a number of features which had been beneficial to power users being removed in the past few years for dumb reasons, but the "they've functionally stolen $3000 worth of games from me" thing is a slightly higher priority on my personal assessment of things.