How can I read a time machine backup on a Windows PC?
Time Machine uses native MacOS file systems so not without extra software.    A possibility untried by me would be the Paragon drivers from https://www.paragon-software.com/home/.  

If you are a bit adventurous you could also look into running MacOS in a virtual machine and let that access your USB-disk.

Safest bet though is to borrow someone elses Mac and let that access the disk.  After mounting the backup image, you can navigate to the latest backup and then the file you need.