I don’t know of a way to directly get a measurement of the iOS file system and APFS snapshot Tidemark storage space like disk utility allows on macOS so I can’t answer your question directly.
Your numbers are typical and don’t indicate a problem or something you’re likely to “fix” or “optimize” further. My iPhone 15 Pro reports 11.68 and 15.75 GB respectively for 17.6.1 and system.
What is known is you need the least space on the device to backup to a computer (macOS or Windows) so when all else fails on low space that’s your last resort to get a good backup. I recommend doing this now to ensure you get AhatsApp data backed up.
Next operation with the least space is an update from computer where it downloads the files needed and applies an update. You would have to wait for Apple to release and update or install a beta on this device to try that to force a cleanup and free space on this phone.
Over the air updates take a bit more space on device.
You are doing the steps recommended above and can keep doing them if you think this will self-correct. Sadly, leaving the device connected to power overnight and connected to WiFi is the best chance to be patient and let iCloud backup get your data backed up. The OS will try to consolidate space and give you back free space, but sometimes you will need to erase the device (either self initiated or from a computer) to get a clean file system and maximize your space available for what should be an operation with enough “free” space.
If you think you could free another 10 GB of application data, do that and wait. I probably would get a computer and erase things at your point. That way you’ll know if it was a temporary “tight spot” the phone landed in or you need to reduce the data you keep on that device.