2020 mac mini running out of hard disk space

I have a mac mini running Big Sur 16gb ram and 250gb hard dive.

Its a work computer but getting not much joy from tech support here.

Its not backed up to time machine fyi, but do use One Drive as storage and backup.

I work on magazine design and I used to be able to store quite a few back issues for easy reference - around 4 roughly. Over the past year I've to reduce what I can hold on machine by quite a bit and now getting to the point where I can just have the issue I'm working on but still running out of space and have to keep running an app called cleaner one to remove some cached files. Also using Daisy disk to help try and remove purgeable files but doesn't really do much. App says I have 138gb purgeable space out of 145gb available but computer is behaving like I actually only have 8-10gb and its not enough to use photoshop much without regular cleaning of some cache files and restarting mac. IT guy says over time the computer will fill up with lots of little files which are spread out all over the mac and are taking up space but little you can do about it. Surely something can be done. I used to store way more than I have on hard drive now with no issues.

So my question is, what do I need to do to free up space. I read things about removing Time machine snapshots but I don't have time machine on. Read something about doing a sudo purge on terminal app but a little hesitant to do that.

Hope there is an answer.

Thanks in advance.