Nowadays I usually just check what's on sale on gog.com, sometimes on Steam, but gog.com has less junk games, cleaner UI and, most importantly, better reviews: I found out that users there criticize more, give lesser ratings and don't hesitate to describe bad aspects; on Steam basically every game, if it's not a complete trash, has "overwhelmingly positive" rating, on gog most popular games have pretty bad ratings. And of course it has lots of old games that I didn't had a chance to play in their era, for example I played original X-Com for the first time few weeks ago.
For a while, I also watched Twitch, but seems that everyone except most promoted streamers got tired and there's nothing except streams of Fortnite. I discovered few games from there, at the times when it was interesting.
My friends are mostly playing AAA games on Playstation nowadays, so unfortunately I lost this way of discovery too.
Might be good to know GOG has a Twitch channel with various streamers that play games available on GOG, quite handy to discover lesser-known games (and quite a pleasant community imho): https://www.twitch.tv/gogcom
For a while, I also watched Twitch, but seems that everyone except most promoted streamers got tired and there's nothing except streams of Fortnite. I discovered few games from there, at the times when it was interesting.
My friends are mostly playing AAA games on Playstation nowadays, so unfortunately I lost this way of discovery too.