Help Recovering From Google HCU

One site of mine got hit hard on the Google HCU in September. I have gone through old content and rewriting it, fixing 401's, 301's, improving metas, and building links. I am stumped at this point. Any suggestions?

if it's YMYL niche, or a product review site you might need to do the EEAT thing. I can't think of anything else that might work as you've covered all of the things I was about to suggest