I know the feeling. I have no advice to offer except to keep on keeping on. It’s a grind, but if it was easy, everyone’d be speaking Japanese.
If it’s any consolation, the kanji that I found impossible to remember from levels 9/10 seem easy to me now. There will always be ‘difficult kanji’ (some level 13 mnemonics are fairly convoluted and … impossible to remember ) but if you continue on, these kanji get replaced with other ones. That might seem like a depressing thought, but it’s actually quite motivating. They won’t stay difficult forever. Trust the grind, it works