stardew valley has some dungeon crawling if you're interested.
dungetris.
dungelot.

unepic.
dungeons of dredmor

the binding of isaac its a great choice..

A few Dungeon Crawlers I enjoy, not sure how heavy they are but they look pretty low end:
The Enchanted Cave 2
Bit Dungeon II
Bit Dungeon+
Deep Dungeons of Doom
Dragon's dungeon: Awakening
Sproggiwood

Different kind of dungeon crawlers:
Dungelot: Shattered Lands
Dungeon Journey

Enter the Gungeon

Take a look at these, I played and enjoyed them, personally :)

Runestone Keeper
Maze Lord
Dungetris
Deep Dungeons of Doom

Darkest Dungeon

Only one of the best games ever made.

I enjoyed watching Dungreed on twitch a while ago :)
Maybe thats something for you :3

If you want something a bit different, Crypt of the Necrodancer is fun.

Shovel Knight is a 2D platformer I really enjoyed.

MiniDoom2: https://calaverastudio.itch.io/minidoom2

• Spelunky (considered to be one of the finest examples of its sub-genre)

• Rogue Legacy (same as the above, I found it quite addictive)

• Darkest Dungeon & Hyper Light Drifter (both a bit more pricey, but well worth the money ofc)

• UnEpic (nice game with tons of stuff to go for in terms of missions, unlockables, etc, lots of funny moments as well)

• Hero Siege (top-down rogue-like with hordes of enemies and loot)

• Super House of Dead Ninjas (I really enjoyed this, easy to learn the basics, but gets progressively harder)

• Dungeon of the Endless (also hard at times, but very well crafted)

• Renowned Explorers: International Society (really fun and surprisingly deep strategic board game - no dungeons per se, but I highly recommend it nonetheless)

https://store.steampowered.com/app/375480/Chronicon/

Blazblue, and I highly recommend you to start with continuum shift if it's your first time playing the series.
Its a fighting game, but with a story and lots of characters with different playstyle

The Swindle is a really good 2d stealth game where you're trying to pull of a series of heists. It really creates a sense of tension like a good heist movie in a way few games succeed at.

If you like weird humor Little Inferno is a wild trip.

Recettear is an adorable old school Japanese game where you run an item shop for adventurers and go into dungeons to get the stuff you sell to them. It's a really cute JRPG.

Not really a dungeon game, but Battle for Wesnoth was released yesterday on steam. It's turn-based strategy released in 2003 and is still getting updates, so it doesn't require a powerful PC. I really love it, and if you like this kind of games you really should give it a try.

I haven't played a lot of Dungeon Crawlers, but I enjoyed Runestone Keeper a lot, pretty straightforward and simple enough to get into, but still quite addictive and fun, highly recommended.

Diehard Dungeon is also quite fun to play

I'll just list my well-perceived "rather-low-spec-2D-games" for you, regardless of genre, maybe you'll find something you can enjoy as much as I did:

• Baldur's Gate I & II - both have a remaster available if your PC can handle it (which isn't too hard to achieve, but having actual 1920x1080 feels really nice)

• Darkest Dungeon -that's already on your radar, I know, still want to mention my recommendation, the game's atmosphere is stunning and the art-style fits perfectly (Early Access buy)

• Dead Cells - IF your machine can handle it, it's a nice follow-up to

• Rogue Legacy - Both games are great Metroidvanias (where Dead Cells is still in Early Access, which I buy very scarcely but this one was worth it)

• FTL: Faster Than Light - Hands down the best 2D game past the SNES era for me... ...I've sunk so many hours of my time into this game and don't regret a second of it

• Jagged Alliance II - Have played the old one when it came out and enjoyed it a lot, have re-bought the Gold Pack a few years back and it didn't catch me for a complete playthrough again, but if you haven't played it yet, it's worth a look

• Ori and the Blind Forest - your machine most likely won't be able to handle it, but holy smokes is that a beatiful game

• RimWorld - this is maybe the second-best 2D game after the SNES era I've played. (Early Access buy)

• Stardew Valley - Already on your radar, just want to give the advice to be careful with modding. My first playthrough was unmodded, for my second one I modded too much, including item generators for convience but exactly this convenience spoiled the fun for me (Early Access buy if I remember correctly)

• Dust: An Elysian Tale - The artstyle may not be for everyone and it might be too hardware-hungry for you,
  but I enjoyed my 100% playthrough a lot and the fact that this game was written, designed and programmed by a single guy is just mind-blowing

• "Tormentum - Dark Sorrow" - got this rather short P&C for cheap, but I liked the artstyle and the occult atmosphere

• Gnomoria - Basically Minecraft flooded with gnomes. Cute game

• • EDIT: Addition: Rollercoaster Tycoon - The good old one in it's purest form. Played it back in the days and had a blast designing coasters in there :)
• • EDIT: Addition: Slay the Spire: I play this via family sharing so it somehow dodged my attention while going through the list - which i'm really sorry for. Regularly updated (almost if not weekly) Early Access game that deserves a recommendation!

This ends my list. I hope you and/or someone else reading this gets a look at a new game for her-/himself.
Have a good one! :)

• Desktop Dungeons
• Rogue Legacy
• SteamWorld Dig 1 and 2
• Crypt of the Necrodancer

You may want to take a look of my post:
https://www.steamgifts.com/discussion/TpRDr/modern-games-that-run-on-a-potato-machine-small-gib-added-level-1-basic-sg-ended/search?page=3

I play on a netbook, so pretty much all my games are low-spec! I don't play many dungeon crawlers, but here are some suggestions:

• Wuppo A cute, funny game with a surprisingly big world and challenging bosses.
• Tumbleseed Unique gameplay. Now that they've adjusted the difficulty I really love this one.
• Pony Island Weird and unique.
• Anodyne Underrated surreal RPG, similar to classic Zelda.
• La-Mulana Addictive, difficult Indiana Jones-style Metroidvania.
• Escape Goat Clever puzzle-platformer.
• GoNNER Procedurally-generated roguelike platformer/shooter.
• Lone Suvivor Survival horror game where you have to take care of everyday needs as well as escape from or fight the monsters. Great storyline and soundscape.

I wouldnt count any game you listed as a dungeon crawler (though I can see why you used the term). However, try Neo Scavenger: https://store.steampowered.com/app/248860/NEO_Scavenger/

Theres a demo available as well.

Not a dungeon, but Dune (not Dune II or Dune 2000, just Dune) is pretty low spec and quite 2D 👀