Slay the Spire is not some random unrelated game. And that was a figure of speech, not an actual game recommendation ;-)
Backpack Hero is essentially a clone of the game Slay the Spire core mechanics. Instead of saying bph is a rogue-like, you could say, it is a slay-the-spire-like.
You walk from room to room, have either fights or events, limited health recovery, bosses give out special game changer items, you must select from rng loot options and build up your inventory of usefull items that work well together. You have 3 action points, and must expend those points between ramping up your block and attacking. The enemies also must re-build their block value every turn and attack you, poison you, curse your inventory, etc.
The big difference is, that you have deck of cards and not a bag of items. And they also have different characters that rework how the game is played siginifcantly. The toad gameplay actually is even nearer to the slay the spire mechanics. You can only loot 1 item, have trouble getting rid of items, and need to draw your items, as if they were a deck of cards.
So again, if you think bph is hard, well, it is. But that is relative ;-)