There's evidence that having super high LDL cholesterol on keto may be fine (do your own research, obviously). Check out https://cholesterolcode.com/ and look up Dave Feldman. Some really interesting research will be coming out soon.
I wonder if OP could continue keto, but go on a statin/pcsk9 inhibitor/bempedoic acid/ezetimibe. Of course, these are prescriptions, so he'll need to find a willing doctor. And have money to shell out. It sucks that he's APOE4/4, since that makes him so much more susceptible to other types of metabolic/cardiovascular disease [3]
0: https://peterattiamd.com/davefeldman/
1: https://pubmed.ncbi.nlm.nih.gov/28444290/
2: https://www.health.harvard.edu/blog/ldl-cholesterol-how-low-...