How long does it take to fix a website to recover from Panda Algorithm penalty?

I have an old sports blog, and I think I was hit around 2013 and my website never recovered since I did have a boost for two years via Discover but after 2021 I no longer appear there.

I still post articles every once in a while, but its a news blog and it has over 7 thousand articles. I was wondering how do I find low quality content, and should I delete them and let them be 404 pages or do I have to just rewrite all of them or fatten the content up all the way back from 2008.

I use WordPress Studiopress Genesis theme, should I just change that and go to Astra theme for page speed?