That sucks. It's integrated fairly deeply with the Zephyr ecosystem and I'm working on several products that use it, some of them fresly migrated to it...

I've made a PR a while back to add support for authenticated attributes and chain certificates (https://github.com/Mbed-TLS/mbedtls/pull/10232), turns out there are several open PRs for that feature set over the years and they just all sit there. That doesn't inspire contributors to stick around.