How can I recover my iTunes library after a Transfer?

My only I tunes library resides on an external hard drive since 2017.

I have always used Windows computers.

Having acquired new I phone 15 pro plus I wished to return the whole library to Windows 10 computer so that the library can be updated and synced/shared with my I phone

i iTunes is up to date on windows 10 and after a few false starts yesterday I finally managed to bring up the library such as it was on screen. However the writing confirmed all tracks etc. were present but all was greyed out and non responsive.

I clicked on files I think and a message appeared to say I will have to download all tracks again! This is nigh on impossible many cds are no longer in my possession and many tracks are backed up in old files and computers. I am now 78 and not at my peak of being able to carry out or even comprehend complicated instructions. My library is or more probably was over 64gb.

I am in uk and wonder what has gone wrong and is it really unrecoverable?

I have read a few threads on here so yes I know I should have had more than one backup but I don’t so no good keep telling me that as many threads seem to delight in informing subscribers! What’s done is done I accept I am a clueless individual but I am still asking for help from those in the know. If all is lost then so be it.

Thank you in advance for any help available.

[Re-Titled by Moderator]