For those that are watching their keywords evaporate, I experienced it for a long time since December core update. I lost thousands of keywords. They are now combing back (months later) at a turtle pace, 2 - 5 keywords per day and not every day. I calculated it will take several years to obtain these keywords back at current speed. I am not sure there is anything you can actually do.
No, there isn't that much you can do, as you (or me, or anyone else) don't actually know what a core update does to a site and why.
All we know it might be several things -
including things not even necessarily to do with your site directly.
Yes, the last part may seem paradoxical, but it does seems to works like that in some cases. For example, G may determine that for certain terms / niches / etc. a certain
type of sites are preferred. Then, if you don't fit into that pattern you get a core update demotion. Nothing necessarily might be
wrong with your site, G just thinks it doesn't fit into the picture they'd like to paint.
Remember, the very first "advice" they gave about core updates was that
"there is nothing you can/should do, there is not necessarily anything wrong with your site. The internet is always changing, and maybe different type of content is now preferred to your bla bla bla...".
Of course, if there are things "wrong" with your site ( think of technical, thin content, spam links, etc.) you should absolutely fix it. But there are zero guarantees it would lead to a recovery.
Yes, I know it's very depressing not knowing what - and if at all - you should be doing to "fix" your site.
I think Google's communication about core updates is very irresponsible. Right now hundreds of thousands of websites are burning (wasting) resources on trying to guess what to do to recover their sites. It's throwing everything at the wall to see what sticks. Most of these will be completely useless and just waste everyone's time and resources.
That shallow thin content blog post from Danny Sullivan from 2019 is not really helping.