What should I do about spammy backlinks from suspect websites reported in Search Engine Console?

If you haven't noticed any problems from these links, you can safely ignore them. Googlebot usually knows how to ignore poor quality links without you taking any action. The fact that these pages now return 500 status means that Googlebot will not be able to see the links anymore either next time it crawls.

Other answers suggest using the disavow tool. However, Google says it is important never to use that tool unless you see a ranking drop that you suspect could be caused by the links. Using the disavow tool without seeing ranking problems is much more likely to hurt your SEO than to help it.