moving company files to another computer using QB 2019 desktop

I recently sold my business and have 2 business accounts on my QB 2019 desktop version on my old office computer/server. I need to move the company files to my home computer. I downloaded QB 2019 desktop onto my home computer, created a QB backup for both companies, and am able to access my newer company (started in 2020) but not my other (started in 2002). It states “unrecoverable error”. I have read other threads and have tried the options suggested without success. I have been having a problem with the backup file based on the fact that my accountant has not been able to open it on his end for the past 2 tax years, so we have been sending him the specific reports he needs as opposed to him being able to access the company via the .qbb file. His IT people have tried to figure out the issue without success. Any suggestions? I am trying to avoid buying the online version due to the high monthly subscription fees, especially since I will be using QB very minimally moving forward.

Thank you