In short your iMac is a bit of a mess and it looks like you bought a base model 21.5" iMac which has a glacially slow 5400 RPM HD. Macs should NEVER EVER EVER have the following types of third party apps installed on them.
- Cleaning apps
- Antivirus apps
- Security apps
- VPN apps
- Maintenance apps
CMM is considered one of the worst and most experienced users on these forums consider it malware. PLEASE locate the developers (MacPaw) uninstall instructions and please uninstall and then post a fresh EtreCheck report. If you have any other of the types of apps installed in the list above, please uninstall them ASAP.
Macs do not require nor do the benefit in ANY way by having those types of apps installed. What these apps do is slow down your Mac (which is slow enough as it is), make Mac OS appear unstable and buggy. They do NOTHING that Mac OS cannot do on it's own. To keep Mac OS fast and secure simply keep it up-to-date and restart your iMac about 1x per week.
Also, you are operating the computer without any type of backup it appears, this is a HUGE mistake and a 150% guarantee you will lose data which could be a catastrophe for you. At the very least you should be using Time Machine which is included in Mac OS. If you are not familiar with Time Machine please click Back up your Mac with Time Machine. This only requires that you have an External Hard Disk, many experienced users prefer the OWC (www.macsales.com) Mercury Elite Pro series fo External Hard Disks.
After you have rid your computer of CMM and verified you have (create and read a new EtreCheck report after the uninstall) then the next step is to use an external SSD to speed up your Mac. In short what you would be doing is replacing the internal HD and using the external SSD as your startup drive. DO NOT think of using the putting Time Machine and your new external SSD install on the same external SSD. This would completely erase why you backup in the first place, use an external HD for Time Machine and a separate external SSD for your internal HD's replacement. You can learn how to install the external SSD by clicking Setup external SSD as startup drive and the drive I'd recommend is a https://eshop.macsales.com/shop/owc-envoy-pro-sx.
Now for the news I'm sure you don't want to hear, in your case what I would do is to replace your 2017 21.5" iMac with a brand new iMac. These are dramatically faster than what you own. Also, an external SSD will cost at least $250, money you could use towards getting a current Mac. I suspect your 2017 will be declared obsolete by Apple sometime in 2024 when they announce the next release of Mac OS. That is a hunch based on the history of what Apple has done in the past. When they declare a machine obsolete that means parts become extremely difficult to find and replace.
If the cost of replacement is a problem, you have LOTS of options available to you, please don't feel you can only use an iMac, any current Mac will work including a Mac Mini, MacBook Air, MacBook Pro, Mac Studio etc. If you cannot afford to all the cash up front, Apple offers 12 month same as cash using ApplePay, something to consider! Also, if new Macs are too expensive, consider an Apple Refurbished Mac. Apple Refurbished devices are great, they are identical to a new machine, have the same warranty as new, are eligible for AppleCare and finally can save hundreds of $$ and you can also use ApplePay to get the same financing as mentioned above. In short an Apple Refurb has no downside.