I have zero problems maintaining Jenkins, and have done so at a couple of different jobs in the past. Minimize how many plugins you use and it works great. We use just a handful: configuration as code, credential storage, kubernetes agent support, pipelines, and job DSL (plus their dependencies of course). Everything is easy to manage because it's just config files in a repo, and things just work for us (with only very rare exceptions).

It would probably be more constructive if you elaborated what your issues specifically were. For example, what have you found pipelines to be incompatible with? I've literally never seen anything they don't work with, so I can't really agree with your assessment without specifics. Similarly, I have zero problem with Groovy. If it's just not to your taste then fine, taste is subjective, but I can't see any substantive reason to call it "a cancer".

This is pretty much my experience too. Working with jenkins is always complete pain, but at the same time I can't identify any really solid alternatives either. So far sourcehut builds is looking the most promising, but I haven't had chance to use it seriously. While it's nominally part of the rest of sourcehut ecosystem, I believe it could be run with minor tweaks also standalone if needed

"Jenkins is the worst form of CI except for all those other forms that have been tried" - Winston Churchill, probably

Least worst compared to what? You think TeamCity is worse?