your rclone mount command is not using cache. your logs show that.
the cache is the not problem.
the problem is that rclone does not support streamed uploads for onedrive, so rclone needs to create a temp file.
note: rclone copy does not that have problem.
gdrive supports streamed uploads, onedrive does NOT support streamed uploads.
basically, when you copy a file into the mount without using cache, rclone does not know the file size,
so this is the sequence of events.
- you copy source file into rclone mount.
- rclone copies source file to temp dir.
- rclone moves/uploads the temp file from temp dir to onedrive