How to go from tech-adjacent to SWE?

It's not a bad idea to try a "whiteboard coding" course such as Leetcode or HackerRank. It's helpful for interviews but also for coding: if you took CS it will help you remember what you forgot, if you didn't take CS you really will benefit. Personally I found HackerRank's Python course to be 100% fun while it sharpened my Python. (Other courses were fine but the Python course had no sharp edges.)

I think the best thing anyone can do is take on ambitious side projects, what they are depends on you. Ideally these projects are fun and self-motivation and build your skills: writing about these projects online and putting up demos is the best thing you can do to get inbound interest short of developing a strong professional network directly. Also if you are talking to recruiters or anybody else you can sound smart, capable and confident if you've got interesting projects under your belt.