TL;DR: see if installing and booting from a Thunderbolt SSD helps. Thunderbolt SSD is the fastest available external bus on that iMac. As a less-expensive option pending replacement, reinstalling macOS with just the pieces you need right now can potentially get you a little better performance. This by purging what you don't need or aren't using.
General...
That hard disk isn't going to be helpful to aggregate system performance. Downhill with a tail-wind, a fast hard disk does 150 to 200 I/O operations per second. You don't have a fast hard disk. For comparison, a slow SSD can do 100,000 operations per second and faster SSDs provide substantially more performance than that.
And you're definitely short on memory for all of what you're trying to use that iMac for.
Booting and running from an external Thunderbolt SSD might get you a few more years. Internal hardware upgrades for 21.5" iMac can be somewhat of a hassle to perform. An Apple authorized repair provider might be willing to swap in an internal SSD and more memory. And even with these upgrades, you're still spending money on a 2011 iMac, and that iMac is not going to run current macOS.
That's a whole pile of apps plus Parallels and MacFUSE and the rest, on what is fairly close to a decade-old low-end Mac. Malware Bytes and iStat and anything else you don't need to be running are all candidates to have automatic startups disabled. And FWIW, your version of Microsoft Office is incompatible with Catalina and later. Silverlight is long gone.
i7 is (was) decently fast for its time, but that box is skewed toward CPU and tends to be lacking in memory and storage performance—Intel's advertising efforts aside, computers are systems, and a computer is only as fast as its slowest part. Not its fastest. Memory is a cache that makes up (somewhat) for slow I/O performance of the hard disk. With little memory and a slow hard disk, you're going to be waiting for your hard disk. Which'll start to beachball
Ten years in computer years is a very long time—if planning to keep a Mac going across most of a decade of software updates, my preference is buying nearer to the top-end of the built-to-order product offerings across processor, memory, and storage.
Here, a decade-old iMac hard disk is also approaching its usual and customary lifetime, and a failing hard disk tends to get slower. (You do have backups going here, which is a good way to avoid data loss on storage failure. Which is good. Keep those backups going.)
For long-term usage of a new Intel Macs, I'd go with 32 GB memory if that's affordable and available.
Macs with Apple M1 are an interesting case here, as Apple is using a new processor architecture (Arm) and a new processor design (SoC) with memory right with the SoC processor, and your choices with M1 are either 8 GB or 16 GB, and I'd go 16 GB.
Apple is also completing the transition of the entire Mac product line from Intel x86-64 processors to Apple silicon processors over the next year or so, so we're to be seeing a bunch of new options arriving, beyond the three new M1 Macs that have already arrived.
What options and alternatives might be offered with new Apple silicon processors and what arrives after M1 we shall learn.
