I have a Samsung A8 with 32GB of internal storage and 32GB of SD. I recently connected it to my PC through USB, and ran a PC disk space analyser on it. Everything on the SD card looks normal and understandable, but the internal storage is weird.
Okay, so the internal file system shows only the storage is only 24.1GB instead of 32GB, I guess that's typical for the games that storage manufacturers play with their sizing practices, I don't care about being shortchanged a little. But it shows that 22.8GB of the 24.1GB is used up. I then fired up the disk space analyser program, and it showed that I'm only using 231MB of space on the internal storage: 104.7 MB for Android, 94.5 for WhatsApp, and 19.0 for logs. The rest are just sub-megabyte numbers. So where is the rest of the system hiding? The remaining over 22GB of stuff?
24GB will be the /data partition, i.e. the user-accessible part of the storage. The actual system software will be in the remaining "8 GB" (in quotes because there are decimal and binary meanings of "G", and different apps are not always consistent in which they use). For example, my "256GB" Galaxy s21 has 225 GB (binary) in the visible part of the internal storage (which would be about 241 GB in decimal units), so the system partitions are using about 15 GB.
No, I don't believe that your system itself is using the "missing" 22GB. But the complex way that Android storage partitions work may not be understood by your PC's disk space analyser: Android uses multiple "virtual volumes" addressing the same space. This allows user files (e.g. your WhatsApp backups) and private data (your apps' internal databases, which only the individual app should have access to) to share the same partition while still controlling access (e.g. the user cannot directly access the apps' databases - before you ask why, remember that the only way you can access them is using an app, and if another app can access them that allows malware to read or alter other apps' data). It's much more flexible than the original system of a distinct "/data" partition (private data) and "/sdcard" partition (public data) with fixed sizes, but it can cause confusion and inconsistent-looking numbers. So for example if your PC only sees the "/sdcard" virtual volume (aka /storage/emulated/0) it is only able to see some of what's in the internal storage. Even then, not all apps can see the size or contents of the /android directory that is within that volume. So I would not panic at all if your PC doesn't know what's going on.
There are android apps that can give a fairly sensible picture of this. The DiskUsage app mentioned above is pretty good. If that still leaves things you don't understand please post a couple of screenshots and we'll see whether we can make sense of it.
Even with root editing partitions is an advanced topic, and I'd approach it with extreme care. I've done it, but only on a device with incredibly little storage and where I was installing custom ROMs that had been trimmed down to fit in a shrunken /system partition. And it wasn't simple matter like repartitioning the hard drive of a computer, it involved editing the binary code of the bootloader (which was scary because if you mess that up the phone is bricked beyond recovery unless you have specialist equipment). So I'd caution against. In any event manufacturers can be generous with the space they allow for the system (gives them scope for larger updates) but not 22GB out of 32GB generous - the problem here will be apps (including updates to system apps) or data, one way or another (this may include data that should have been cleared up but the system has lost track of).
Basic questions: how much space does your phone storage menu say you have left? Have you tried clearing app caches (browsers can cache hundreds of MB without telling you)? One particularly nasty feature of the System > Apps menu these days (or at least on my Galaxy) is that when you look at the list of apps it tells you the size of the app and its data but excludes the size of the cache. So if I look at that list I see "Firefox, 375 MB", but if I click on it and scroll down to "Storage" I see "868 MB used in internal storage" - the 493 MB difference is the app's cache, which they hide away from you. I can only assume that they are trying to stop people from thinking about (and clearing) caches, but it's not helpful.
