itl file corrupt after update and no previous version of itl created

Hi,

Details:

Laptop running Windows 10 home, 20H2 update

iTunes music files stored on NAS, nearly 950GB

I updated to iTunes 12.11.0.26 last night (24th), when iTunes was opened for the first time, I only had a handful of purchases showing. Ok, fine, I need to point it at the old itl fine. Looked in the previous libraries folder, the last version was created in 2018! Nothing since then, I've not had issues with the library file before now, so never checked after updates to see if one was saved or created.

Quick forum search, followed this https://discussions.apple.com/docs/DOC-6561

renamed the last saved temp file (dated 23rd, size 54806 KB) as a new itl file, hold shift, open iTunes, point it at the new itl file. Message - 'The File does not appear to be a valid iTunes library file' New itl file - (damaged) library created'. (Note at 54806 KB)

I've tried another laptop, with iTunes 12.10.4.2, pointed it a newly renamed temp file, same issue, invalid/damaged file.

I have a manual external back up of all files and libraries from 11th Nov. But the library file is dated 26/10/20 and only 8294 KB, this seems to small.

I do have an XML file at 54190 KB though saved here. (no XML file in the current iTunes folder)

Anyone else had this issue? What's my next step?

Downgrade iTunes and use the small itl file from 11th? Then run iTunes Folder Watch to reload anything added since October?

Use the next temp file created on 12th Sept. (32768 KB) with a downgraded iTunes? Or the current updated version?

Do something with the old XML file?

Plus how do I force iTunes create a previous library on the next update?

Thanks for reading this far and for any help!