Thank you very much for analysis. (You too @Owl-53.) It is very much appreciated. Glad I gave into my anxiety and asked for help rather than going forward.
Running through your points:
1) Yes, there's a lot of Word documents on this tiny laptop. While I do have an iCloud Drive account, I prefer to work off the hard copies. I have been thinking about getting another external hard drive purely for my writing / work, so I could move the all of the files across onto that and work primarily off for the hard drive to free up room. Along with taking a look at the other storage-freeing solutions.
2) Hopefully doing the above will improve the Write Speed. I'll run another report after I've moved some files around to see there's any improvement.
3) Honestly had no idea about Bitdefender. Thank you for the heads up - I'll delete it.
4) The reason why One Drive is crashing is because my OS is too out-of-date for it to work. I previously used this to work on work-related writing both at home and in the office as my preferred writing software is Microsoft Word. I keep an external hard backup and iCloud Drive though, so deleting it shouldn't cause any problems. Regaining access to this was one of the reasons why I wanted to update the iOS.
One last questions if I may - do you think I would be better off upgrading Catalina to either Moneterey 12 or Ventura 13? Still getting some of the upgrades I need from a piece of software my laptop can properly handle.
Thank you again for all of your help!