What’s the best way to back up my PC to Google Drive before a clean install?

The simplest option is Google Drive for Desktop. Install it, choose the folders you want to sync, and let the upload finish before reinstalling Windows. After the clean install, download the files from the Drive website first rather than immediately reconnecting the sync app, so you don’t accidentally mirror an empty folder and delete the backup.

Tools such as rclone or Cyberduck can transfer files to Google Drive, and some can present cloud storage like a regular drive. They may be useful for large batches, but the actual upload speed will still be limited by your connection. Also, Google Drive shouldn’t be your only copy of anything important.

Don’t assume that copying a few personal folders is a complete backup. Important application settings and data can be stored in less obvious directories. Either make a full system backup or carefully identify everything you need, and verify that the uploaded files can actually be downloaded before wiping the PC.