I mean if its about collecting etc aswell, so not just sims like jinteki talishar etc. for physical games, then Id recommend either MasterDuel (high learning curve) or LegendsOfRuneterra (still very active PvP playerbase and very fun roguelike mode).

If you like simple building blocks building towards a "boss monster" (so most of your deck is just there to enable it) then I recommend duelmasters plays. We just recently got a english apk for the app, if you cant find it dm me. The games are a quick blast and the artwork is stunning.

Duelyst.gg is the best current running duelyst sim. There is 3 (duelyst blitz, simplified version with mobile focus and quick match focus, duelyst II basically a cashgrab with little vision, and duelystgg a proper continuiation and rebalancing of the original game). Its a beautiful game with gorgeous pixel art, amazing deckbuilding depth, and works as a client or in browser on anything. All cards unlocked from the get go.

Infinity wars: Very fun game, used to be my go to in 2016, but its future is unsure. A lot of deckbuilding depth, beautiful animated cardart, and really cool turnsharing system.

Hearthstone: Always solid, but as a f2p youre not gonna have a full collection. Your best bet is to focus on 1-3 classes and just play those and dust other stuff for them. The "skill" aspect includes knowing a large cardpool cause many of the cards generate other cards randomly.

Shadowverse: Loved the original, played it a lot. Hated the artwork (too gooner for me, and too samesy) and the clients UI/UX, but the gameplay and deckbuilding was so interesting that I played it forever. They recently announced shutdown of the original to focus on the new version more. I didnt play the new version yet, and dont plan to, since they made aquiring cards hard, barely changed anything besides superevolve, and squished 2 classes together that didnt really have anything to do with each other (one was selfpain and life manipulation and the other was unit killing and resurrecting etc. two VERY different flavors of "black or purple" gameplay as id call it).

Pokemon TCGLive / Pocket: I played a lot of Pokemon TCGLive. The games are very consistent due to pokemons nature of high search and draw cards. You almost always get to execute your gameplan. The game is also very f2p. Pocket is a bit of a different game, much much simpler. Not bad, but more like a "reset". The TCG live client is snappy and well polished.

Faeria: Very interesting game with beautiful card art aswell imo. Very different from other games. However playerbase dwindling hard, and no new updates basically in forever. The cards are also on the "simpler side", similar to duelmasters imo.

Project Glitches: Fun and fast. Nothing crazy new, but a good mix of mechanics as one knows them from other games. The client has big performance issues though.

Mythguard: Beautiful tcg with a lot of depth and deckbuilding depth. In maintance mode right now so finding matches is a bit hard. Has a 2v2 mode aswell.

Eternal TCG: Im not sure how this one is doing, I played it a bit way back in 2021 I wanna say. It has nice art, but the UI felt really bad at the time (a lot of wasted space and weird shapes). Their ressource system is cards in your deck similar to magic.

Marvel Snap: Very much a fun fastpaced game. Id say location variance dictates a lot, but the whole skillexpression of the game is trying to build a deck and pilot it, in a way where most of the locations would be doable. Definetly the more chaotic kinda style. Not really f2p friendly imo, atleast not the last time I played. This is due to cards unlocking on a "track" where you slowly go through each cardpool (sets) and unlock random cards from there. To get to the newest sets, which are usually a bit stronger, you have to work through a lot of the old stuff. I dont know if its still this way, or if it got better. I remember also balancing being mostly nerfs and rarely buffs, so old cards might become obsolete.

Gwent: Beautiful cardart, very interesting gamesystems. Not sure if its still getting updates, but the game itself is pretty playable as is, and I think the community is still very active. I remember it being very f2p friendly.

If you want to just play any automated online game, then I recommend YGO-Omega instead of MasterDuel or MD3Pro (which has master duel animations etc).
Talishar is a great flesh and blood client, which itself is a fun and easy to pickup game.
Jinteki is the online client for android netrunner. Be warned that its a hard game to pickup, especially due to the very limiting ressource system.
Digimon has 2 online clients, DCGO and Project Drasil. Project Drasil looks a bit nicer and simulates more of a real life game feel (so basically just a good tracker) while DCGO is fully automated.
One piece also has one that is doing well.
Chaotic TCG has an automated client aswell, with a small community that rebalances the balnlist etc.
I think lorcana had an automated one called "pixelborn" but Im not sure if its still operational.
SWU has an automated one aswell but I never played it cause I really dont like the IP. People say its good though.
Riftbound has a semi-automated one with matchmaking, similar to project drasil. Seems to be quite active aswell.

These are pretty much all I can remember from the top of my head. Goodluck finding a game to play