Different companies have different approaches on how they inform their users about changes in ToS. Update channels can be on their platforms with a pop-up announcement, through email notification, on social media channels like Telegram, Discord, X, Facebook and more. Some platforms have their Change Log pages for noting down important changes on their platforms.
As said, companies have diversifying approaches and there is no standard on how a company should or must do it. Personally, more transparency in big policy changes should be better and it also shows how a company respects their users and treat them fairly enough.
But to make it formal, emails are the common use informing users, which is widely used for all the services i used (so far). Social media channels are just used for announcements. And ToS changes are announced in advance and will only take effect after few days or weeks, Stake used this approach and some of the known services i
an'm using
which i guess the most legal way.