How can I improve as fast as possible?

The startup I'm currently a co-founder of is running out of cash. Although I'm on great terms with one other co-founder the other has had some mental-health incidents that are straining the company to it's limits.

I've been doing startups for a few years and fortunately have some exits, but as a result my resume is somewhat scattered. I have a number of successful and unsuccessful stints at growth stage startups both as a SWE and technical product manager.

My issue is I have some dental procedures I need to have done and for my own mental health want to take a year or two just to work as a software engineer at a well established company.

Obviously the market is a tad rough at the moment, but what I've realized is that I'm not sure if I fully hold up to the current above avg bar for SWE's (enough to get hired without too much of a grind).

As a late 20's engineer does anyone here have a suggestion for how I can upskill as soon as possible to get a SWE job as someone without a perfect background or a FAANG background?

Any help here is immensely appreciated.