Well spotted.
We do check for Retry-After headers but only on 429 errors.
A read of the docs indicates we should be checking on 503 errors too!
Please give this a go
v1.69.0-beta.8356.c02c3c013.fix-onedrive-retry-after on branch fix-onedrive-retry-after (uploaded in 15-30 mins)
This should hopefully help a lot with onedrive throttling which has been bothering rclone users for some time.