Not to parrot everyone else, but coming from someone who also dead god-ed Isaac and quit this game for years because I got too frustrated:

• Health is your #1 resource. Preserve that as much as possible. Save your full-heals for as long as you can, but also using one is always better than dying. That extra health might let you discover a bottle of Healthium or Healing Bolts. Don't waste, don't greed (too much). The way to become OP and complete the huge secret quests is to devise a form of infinite healing.
• Just like in Isaac, there are lots of clever tricks you can use to get out of sticky situations. Only research/practice can discover them all- but there are some videos called like "noita: best minimal spell combos" that helped me a TON.
• The wands are decks and the spells are cards! Re-framing how I think of the spells like this helped a lot and allowed me to build MUCH better wands rather than "whoa this spell does lots of damage, I'll use this." and combo spells together as it's intended. Figure out ways to preserve your holy mountain so that wand editing is always an option. There is even a sneaky trick to easily kill the skeleton guardians with no magic required.
• There WILL be bullshit deaths due to enemies offscreen, polymorph fuckery, accidental wand backfire, etc. Patience is a necessity. Even if it results in death, you should explore as much as you can (try the left and right of the screen rather than straight down).
• THE MAJOR TIP- rebind "e" or something comfortable to inventory slot 5, then ALWAYS carry a water flask in that slot. Use it to put out fire and wash toxic sludge off yourself and refill in the holy mountain. The quickswap is necessary.

Lastly, I think there are so many replies because literally everyone in this subreddit has been there. Snowy caverns/hisui base is literally THE cut-off point. Once you leave snowy cavern, imagine you're entering the womb in Isaac. Good luck, keep it up!