Cannot access files to delete

I currently use freefilesync on ubuntu 24.04 to back up my data. A couple of months ago I started to get errors on the external backup disk that a quick (and ineffective) look didn't resolve so I just ignored them. Today I delved deeper. If I use Files to open one of the problem directories it gives an error "This location could not be displayed" with a file name stating: input/output error. Double Commander (my preferred file manager) opens the directory fine but shows no files. However, using ls -l in a terminal lists a number of files with reasonable file names but where the attributes, owner, group, etc should be listed there are only question marks. Unsurprisingly attempting to run chmod, chown, rm, etc just results in an imput/output error. I also tried to check the partition with GParted but it crashed, Is there an easy way top resolve this issue? I suspect the best option is to bite the bullet and reformat the external disk and backup my 2TB data from scratch. My only concern is that, despite knowing better, I have just the one external disk so would be without a backup for a short while. Any suggestions gratefully received Keith