Without a dropping a resume...I do back-end in Java/Clojure, React based front end. Domains include automated file transfer and telephony. I can learn whatever if it doesn't require a PHD.
Honestly, my passion/interest/strong suit is tackling problems that matter, and if that involves using a broad swathe of my skillset, all the better. Clojure is probably my favorite language, but I don't fetishize any particular technology. For what it's worth, I don't mind/actually like working on crunchy old legacy code. Often a lot of the business value is tied up in that, and someone has to know how to get in there and make it work.
If you have these skills, a vague passion, and some time/cycles -- its your best interest to:
1. More learning
2. Seek out a local group aligned with your passions that can benefit from your skills See #1.
3. Contract work.
4. Side Hustle project per your passions, or whats gleaned from #1
5. Create a new thing, with your skills, and your passion, what can be built around such - where you require minimal inputs to output MVP/A Thing/etc
6. And finally - or even #0 --> build portfolio New Job.
If you would like some side-project ideas just for portfolios sake, based on the zero I know of your backend cap[abilities, Id be happy to provide some starter ideas - which are needed, but may not result in revenue - but can showcase your skills.
Honestly, my passion/interest/strong suit is tackling problems that matter, and if that involves using a broad swathe of my skillset, all the better. Clojure is probably my favorite language, but I don't fetishize any particular technology. For what it's worth, I don't mind/actually like working on crunchy old legacy code. Often a lot of the business value is tied up in that, and someone has to know how to get in there and make it work.