I can see what is happening there...
Rclone issues the DELETE on the directory
2020/09/12 22:44:36 DEBUG : HTTP REQUEST (req 0xc00066b300)
2020/09/12 22:44:36 DEBUG : DELETE /v1.0/drives/b!-Jr3ZPe__kCZ7xLdl2FMoffWFSmIUF1AoWygTwxjtywWlD7heAFZQpK_8QbDA7ff/items/01HSWNV2LEGZAH5A2BLJE3R3I4ACF3QDRK HTTP/1.1
Host: graph.microsoft.com
User-Agent: rclone/v1.53.0
Authorization: XXXX
Accept-Encoding: gzip
The server responds with a redirect
2020/09/12 22:44:36 DEBUG : HTTP RESPONSE (req 0xc00066b300)
2020/09/12 22:44:36 DEBUG : HTTP/1.1 302 Found
Cache-Control: private
Client-Request-Id: 9f245298-ad4b-4c78-b6c3-478208784d04
Content-Type: text/plain
Date: Sun, 13 Sep 2020 02:44:35 GMT
Location: https://redacted-my.sharepoint.com/_vti_bin/client.svc/v2.0/drives('b!-Jr3ZPe__kCZ7xLdl2FMoffWFSmIUF1AoWygTwxjtywWlD7heAFZQpK_8QbDA7ff')/items/01HSWNV2LEGZAH5A2BLJE3R3I4ACF3QDRK
Request-Id: 9f245298-ad4b-4c78-b6c3-478208784d04
Strict-Transport-Security: max-age=31536000
X-Ms-Ags-Diagnostic: {"ServerInfo":{"DataCenter":"North Central US","Slice":"SliceC","Ring":"3","ScaleUnit":"003","RoleInstance":"AGSFE_IN_30"}}
Content-Length: 0
So rclone does the request at that URL
2020/09/12 22:44:36 DEBUG : HTTP REQUEST (req 0xc0004be400)
2020/09/12 22:44:36 DEBUG : GET /_vti_bin/client.svc/v2.0/drives('b!-Jr3ZPe__kCZ7xLdl2FMoffWFSmIUF1AoWygTwxjtywWlD7heAFZQpK_8QbDA7ff')/items/01HSWNV2LEGZAH5A2BLJE3R3I4ACF3QDRK HTTP/1.1
Host: redacted-my.sharepoint.com
User-Agent: rclone/v1.53.0
Authorization: XXXX
Referer: https://graph.microsoft.com/v1.0/drives/b!-Jr3ZPe__kCZ7xLdl2FMoffWFSmIUF1AoWygTwxjtywWlD7heAFZQpK_8QbDA7ff/items/01HSWNV2LEGZAH5A2BLJE3R3I4ACF3QDRK
Accept-Encoding: gzip
However it has turned the DELETE into a GET request...
After a lot of thinking, I think this is actually a bug in the go runtime and I've reported that here.
Ideally Microsoft should be issuing a 307 redirect here which means don't change the HTTP verb. I think Go's behaviour in changing the DELETE is wrong though.
You can do this with rclone by using the --disable Purge flag which stops the special purge method for onedrive running and rclone will revert back to iterating the directory and deleting things individually.
It is possible to make a workaround for this if you are desperate - let me know!