Jira is absolutely huge, so it's hard to tell what parts of it you're interested in.
I haven‘t used it myself, though
Can be easily extended and unneeded fields can be disabled via template.
We use it since 20 years at a 6000 heads company and it's totally fine.
https://ekso.app
Fully self-hosted, dockerized.
We made the pricing reasonable -- YMMV.