Mostly city builders and other management games, turn-based strategy games, and also pinballs.

Stardew Valley is definitiely like this for me, in addition to most games in the Soulslike and rogue-like genres :D

What addictive and relaxing game I want to play depends on what genre I'm in the mood for. Among the ones available on GOG...

For an arcade-y game, Super Puzzle Platformer Deluxe.

For a micromanagement game, Train Valley 2.

For a card-based game, Guild of Dungeoneering.

For a sandbox game, Terraria.

For a farming game, Stardew Valley.

For a "driving" game, Race the Sun.

For a tower defense, Defender's Quest.

For a rhythm game, Crypt of the Necrodancer.

For a roguelite, FTL.

When I'm in the mood for a sim/tycoon game, OpenTTD is one I have to be careful with because I can easily wind up staying up hours beyond bedtime on it.

There are genres where my choice is a non-GOG DRM-free game (eg. Hexcells Infinite for a puzzle game), but I think that list is already long enough so I won't go exhaustive.

Really? Nobody said STALKER already? That of "play just a few minutes doesn't exist, when you enter The Zone, you never know when you're gonna leave...

For me it's usually turn-based, strategy and/or managerial types. Civilisation is the first thing coming to mind. "Just one more turn..."

I found it hard to put the controller down in Elden Ring too. There is always something more to explore.

And I stumbled upon Vampire Survivors, which I start up for just one game and only stop hours later when hunger becomes unbearable.

Slay the Spire. 565 hours in, and I still think "I'll just play to the first treasure chest."

My vote for Islanders as a similar relaxing, city-building puzzle. Very minimalist, however I can spend hours with it.

Mindustry

Slay the Spire and Roguebook....just one more battle and hours later still going lol

Need For Speed: Most Wanted (2012). I would most often start the game for a short ride, maybe a police chase. Drive to airplane graveyard to check highscores between me and my friend (him being offline most of the time due to different time zones). And I would find that he has beaten every highscore of mine. So, naturally, I would beat his and leave the surprise. Eventually we could no longer beat each other, so repeat same competition in different areas.

As for GOG store specials, The Witcher Adventure Game. I swear, there can be a year since last play-through, it can be last evening, yet it is always the same - "Well, haven't played this for a while. One quick game". 2 hours later, on n-play-through and settings for the longest game - "I CAN DO BETTER!!"

I feel just about any game is like that for me...
Starting with the original civilization back in the day. Probably even before that on the Atari.. with pitfall. Moving on thru one fast non dying run in contra, one quick level skipping run in super Mario, just one quick game of techmo bowl before moving to pc gaming and doom, diablo, c&c, civ, homm franchises. To present day xcom2, slay the spire being my recent addictions.
And so many more over the years. Gaming has always been a fun, and super enjoyable hobby. Less time for it now obviously but you never ever get too old for it. And it always transports you back into that teenager from so many years ago mentally. How can anyone play for just 10 minutes?

Shin megami tensei V. I was already a huge fan of the smt/persona series but the introduction of open-world gameplay makes it more difficult to find a good place to stop. I had a stretch where I played 28 hours in just 3 days and I still wanted to keep going. I had to force myself to put it down.

Hades and You Must Build a Boat come to mind, mostly because of the same reason: overconfidence that next time I'll do better.

Come to think of it that also was the drive to continuously start a new character in Realm of the Mad God.

Townscaper.

I always end up spending way more time "relaxing" than I initially planned XD, because of how simple and straightforward that game is.

It's also so so similar visually to Dorfromantik!

The Civilization series.

I think to myself, "just one more turn", and before you know it I've played for tens of years.
Q: "Hold on, tens of years in-game time or real-life?", Answer: "Yes."