How to reach a wider audience?

Hey there - so I make illustrated books instead of heavily written books and realistically, I'd have imagined the customer base would have been slightly bigger due to recent trends and the fact they're interactive and calming (they're c0l0uring books but I'm not sure why I can't write that word in this sub).

Nonetheless, I'm an artist and illustrator who's worked with multiple publishers and has been on KDP for years. I have a small audience but realistically not enough to bring in a sustainable amount every month. I uploaded my first book 3.5 years ago and it did well, then a second, etc. I have plans for more.

Well - I F'ed up badly. When sales were good (like £500 a month good with less than a year on KDP), I decided to try reduce print costs by going in and amending the settings/paper quality and print details which obviously made me unpublish the original listings and redo them. Stupidly, at the time, I didn't realise this would reset the entire algorithm.. and all of a sudden my books with like 30 x 5 star reviews and making me consistent money every month, then made me none because I'd made a mistake.

I feel awful and have since. For the past 1.5-2 years after this indicent, I've tried my best to get them going again. Republishing the original listings did nothing. Changing prices temporarily did nothing. I have 2 instagram pages advertising my art and these books with no luck. Once people buy a book, they don't typically buy duplicates. I take copies to markets, but again, this isn't helping the Amazon algorithm.

I'm not sure what to do anymore. I have 5/6 books now, the covers are all hand-done and look awesome, the insides are all hand-done by me, no AI, nothing. But I'm sadly only earning between £20-100 per month and that's being generous.

Any ideas? Are Amazon KDP ads any good? - as they look very complex to setup.