I had odd side tasks at a few previous jobs that while I couldn't automate them per se, I created some combination of spreadsheets and parameter-driven drawings/models that greatly reduced the time and all but eliminated errors.

The first time I did something like that, I was young and dumb and showed my boss and their management team. As a reward, I was given a ton more work and expected to do it all in less time, even though what I'd created was only applicable to about 10% of it. Then when I couldn't meet that workload, I was berated and had my "helper" spreadsheet and drawing made fun of in a meeting.

After that I made a similar sheet to help on a different task and only told a coworker friend...who then proceeded to tell management about it and take credit for making it. Karma being a bitch, though, he was just given more work to make up for that efficiency as well, and a few months later some of the variables changed and he was totally unable to fix the built in formulae to account for it, so it was basically useless to him, but he still had the work.

After that I just never told a soul about anything like that until maybe if I was leaving the job.

At my very last job before my current one, I had developed a 3D model that accepted a string of about 30 parameters and, as long as there were no conflicts, spit out a model that was 95% of the way to complete for maybe 60% of my normal workload, and as long as it was successful, it came with an associated drawing template that also auto-populated most of my work there...so basically taking a little bit over half my normal work and making it at least 75% faster. A game changer.

I sat on that shit for the last 9 months I worked there, using it, improving it, adding features on my own time, troubleshooting issues, etc. Said nothing to my boss or my one other coworker until literally the day I gave my notice. I figured it'd help my coworker handle the increased workload until they hired my replacement (but didn't want that asshole to get credit for my work) so I showed both him and my boss at the same time.

At first, both acted unimpressed and uninterested. After a few days though, my coworker was using it and quickly they realized the value. Instead of thanking me and asking how it worked and could be improved, they just told me "Use the time you have left to improve this to work on every possible variant of the type of part it works on, and also develop an equivalent for the (totally different) type of part your coworker makes. Have it done before your last day."

I had like 4 days left.

So I literally just said, "No, not going to do that. It took me months to get this one where it is, and it's stable and works on most cases. Trying to add that much to it in 4 days might break it. There's just not enough time, so no, I'm going to finish my backlog of work and clean up my desk area for the next few days and that will be it."