Ram fills up a lot faster than usual

Note that when you run out of real RAM, it starts to use a Swap File on your hard drive, with a slow 5400 rpm HD, that will be a noticeable performance hit.

8 GBs of RAM is a pretty minimal amount. Upgrading it to 16 GBs of RAM, if possible, and replacing your mechanical HD with an SSD will speed things noticeably, especially the SSD upgrade.

I'm a long time computer - Windows, Mac, Linux etc - user (since 1981) and I've never installed anything that 'helps', or "speeds up", or "fixes" etc as they're all designed to (1) extract money from you and (2) be self-serving so as to justify their existence and keep extracting money from you.

IMO CleanMyMac is one of the worst as you don't need it. Simply shutting down your computer regularly will do all the "cleaning" your Mac needs. Occasionally applications and/or their preference files may get corrupted as time goes on which is why I recommend, backing up, reformatting and reinstalling a clean OS every year. Think of it in the same way as your car or central heating system. Performing regular maintenance/service checks goes a long way in keeping things in good shape. Prevention is better than cure.

There are lots of programs out there that are designed in the same way and yes I would consider most as crap. Judging by what you've said it sounds like you would benefit from upgrading your drive to SSD. You would see an immediate and impressive improvement in speed and capabilities. Instead of waiting 1-2 minutes or even longer from boot to desktop you would see the same process in 30 seconds or less.

Etrecheck is great as a diagnostic tool and it may reveal more but ultimately if you want to run the latest macOS move to a SSD sooner rather than later.

Good luck.

Welcome, Boris-S-Wort, to Apple Support Communities!

First, you need to remove CleanMyMacX from your machine!

Most of us, here (and we are but users, like yourself) consider the CleanMyMac programs to be on a par with malware: malignant software.

Second, what is this archaic obsession with how much Free RAM there is?

You paid for that RAM! If it isn’t being used, you have wasted your money!

My Mac mini has but 8 GB of RAM. It is almost always being completely used!

I would expect nothing less!

My only concern with increasing my RAM size (I can go up to 64 GB) would only be whether I might buy more than I actually need!

However, I’m certain that before my Mac mini is done, I will be using the full 64 GB! (In fact, based upon my experience with the technology, I’ll probably be at 128 GB before the mini is done! [My old MacBook was only rated to a maximum of 4 GB, but it is running 8 GB, for a few years now, with no issues!])

The main thing you have that is leading to «it slow[ing] to a crawl» is CleanMyMacX.

A secondary cause could easily be a slow Hard-drive! (Even if it isn’t failing!)

Is the hard-drive, in your Mac mini, an SSD, a Fusion drive, or an old spinning disk (hard-disk): listing from fastest to slowest?

Besides removing CleanMyMacX—according to manufacturer’s instructions—I recommend running the Free version of Etrecheck - the handy reporting tool for … - Apple Community, and posting the generated report, here, within a comment, using the “Extra Text” button.

There are many of us that can help you interpret that report.

Make sure you buy the amount of RAM and SSD for your future needs, as often they cannot be easily upgraded, if at all. All new Macs come with SSDs, but make sure you get one large enough to meet your future needs. Having a portable Mac that needs an external drive to operate normally is no longer that portable.

Agree with Boris, CleanMyMac is junk.