Trinity Fusion is a roguelite Medroidvania game released at the end of 2023 by independent developer Angry Mob Games.
I'm a casual gamer and I find it a very difficult game.

The "Trinity" in the game is the trinity of essences that make up Prime and which were each given an unnatural boost in the three other universes. Each of the others started out as a copy of Prime but diverged.
The essences and their repercussions are "Life" which resulted in runaway wildlife that killed everybody, "Pattern" which resulted in intelligent machines overthrowing their human masters, and "Mind" where everybody is a cyborg.

The four "universes" are still loosely tethered together, but there is a looming catastrophe that might destroy or unite them all.

You start in Prime as "Maya", the only person left in Prime with duplicates in all three other universes. You'll have to borrow their bodies and their unique skills to stop the bad thing from happening.

Your other selves (distinguished by different name, hair colors, outfits, and weapons) include a melee version, a ranged version, and a techno-mage version.
Also, one of them has double-jump and one has wall jump, but I can't remember which is which.

Aside from the universes threatening to "fuse" back together violently, the other "fusion" bit is that you eventually unlock the ability to "fuse" two alt versions of yourself into a combo unit with all the features of both (and another new name for each possible combo).

And you will die often.

As I said earlier, I find the game very difficult. The enemies hit hard and your dodge mechanic is not as forgiving as in some other games without specific powerups.

As for difficulty modes, the game has three.

They call their "normal" difficulty, "Veteran" and I did not last a minute at that difficulty.
I had to drop down to "Surivor" difficulty which makes the enemies weaker and gives youa few boosts.
I still couldn't make it past the first stage.
I had to enable "Hyper Mode" which, similar to "Hades" God mode, gives you a extra boost to defense each time you die. It's 15% up to 65% in this case.

After about 20 hours of that, I was able to switch to "Veteran".

I'm currently at 64.7 hours and have all but 1 achievement unlocked.
Unfortunately, I do not think I will ever get it.
I have to win a game on "Hardcore" difficulty.
Hardcore isn't just "enemies hit harder". Hardcore radically changes a few elements of game play such that just getting hit too many times, even if you have plenty of health, will end the run.
Also, "Hyper Mode" doesn't work in "Hardcore" difficulty.

Its a fun game and I like it. More people should play it.

Hardcore Mode

Unlocked after completing a successful run on Veteran difficulty.
More than just a difficulty option, Hardcore mode is basically its own game mode. We HIGHLY recommend trying it out once you have a feel for the game. It’s honestly become our favorite way to play the game in the studio.
Enemies will increase in difficulty the longer you stay in the same biome. A timer ticks down on the right hand side of the screen at all times, letting you know when the enemies are about to get tougher. Clear stages quickly, or you might have trouble.
Maya’s link to her counterself can be disrupted by enemy attacks. Take too many hits in a row and you’ll be sent back to the Citadel, regardless of what your remaining HP is.
More support enemies will spawn per location. Enemies whose jobs are to buff others will appear more often, turning otherwise normal encounters into chaotic scrambles.

Edit: It's Steam Deck certified and ran fine as my LCD model and again on my OLED model. It didn't originally have a Steam Deck preset and performance could jank in some instances, but since they became fully certified and introduced a preset, it runs great. No further issues.