Unable to use Quick Start for new iPhone, also unable to back up to PC or iCloud

Hi, have looked around for answers to this but haven't been able to see any (I welcome being shown any!). I have also contacted Apple web chat for support on this but they have been unable to suggest anything.

Short summary: I am unable to use quick start to transfer data from old iphone (8) to new (11). Just get "Preparing to transfer" and no progress then "Data Transfer Cancelled". Backing up to PC stopped working recently and I can't back up to iCloud either. iPhone running latest iOS (12.4) and PC running newest version of iTunes. As much info as I can think of below in case it's helpful (apologies for length!)

Last week after ordering new iPhone I went to back up my old one in preparation. My previous last back up was mid July. iTunes on my PC was unable to run any back up or sync. It would get to stage of "backing up", go straight to 100% complete blue bar and not return to the beginning (waiting for 30 minutes plus to ensure it wasn't just a matter of time). (in this time I also updated iTunes to latest version and at one point had to reinstall the driver for iPhone 8 as this was an issue after the update to latest iTunes).

To try to use an alternative I bought 200gb of iCloud storage (having never used icloud before) and attempted to back up there. The automatic background backups failed and when I have tried to run a manual back up this would simply start at the beginning of status to upgrade but never show any progress (even left for hours/overnight).

Today I picked up new iPhone 11 and was hoping that despite these difficulties I might be able to do the quick transfer. Unfortunately the quick transfer (both devices next to each other, same network etc) is very much the same. I'm just getting the spinning wheel and "preparing to transfer", for a time then "data transfer cancelled". On one occasion it just kept on "preparing to transfer" until I cancelled it after over half an hour.

Old iPhone is an 8 running iOS 12.4 (this is the version Apple chat support has recommended).

Old iPhone 8 had been experiencing a few problems recently - crashing or not properly loading games which require a lot of processor power. I put this down to an old bit of hardware running newest iOS as this was much more pronounced after an upgrade a couple of weeks ago. The only other issue is that a chunk of my photos (couple of years worth) still have their data on the phone but don't appear in photo stream/app. THis has been the case for at least a year and hasn't caused any other issues - I have them backed up to PC and can see them in windows explorer if iPhone is plugged in. But I wonder if it is indicative of an issue with the phone's storage?

PC is old and low on storage (60gb free currently) but that was the case in July when backups ran well (and I would expect to get to an error message about lack of storage?). I've checked previous back up files (and deleted all except most recent to free up space) and back up files are much smaller than the space available.

iPhone is a 256gb model and has 195gb used. Storage used was MUCH higher previously and would back up without issue (other than taking a while...).

I have tried to back up just my photos to iCloud to free up storage on phone and see if that improves anything but same issue - trying to start upload but never moves onto anything (and basically freezes up the phone, unable to open most apps, similar happens if I try to run a back up).

Sorry for length but wanted to get as much detail in to answer people's questions ahead of trying to help. Really appreciate any support, especially as there aren't any available local Genius appointments for a full seven days.