Here it goes (the password is deliberately hidden):
$ rclone lsd -vvv --dump headers,bodies mailru:
2022/10/26 10:00:44 DEBUG : rclone: Version "v1.60.0" starting with parameters ["rclone" "lsd" "-vvv" "--dump" "headers,bodies" "mailru:"]
2022/10/26 10:00:44 DEBUG : Creating backend with remote "mailru:"
2022/10/26 10:00:44 DEBUG : Using config file from "/home/dma_k/.config/rclone/rclone.conf"
2022/10/26 10:00:44 DEBUG : You have specified to dump information. Please be noted that the Accept-Encoding as shown may not be correct in
the request and the response may not show Content-Encoding if the go standard libraries auto gzip encoding was in effect. In this case the body of the request will be gunzipped before showing it.
2022/10/26 10:00:44 INFO : []: Valid token not found, authorizing.
2022/10/26 10:00:44 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2022/10/26 10:00:44 DEBUG : HTTP REQUEST (req 0xc00017c300)
2022/10/26 10:00:44 DEBUG : POST /token HTTP/1.1
Host: o2.mail.ru
User-Agent: rclone/v1.60.0
Content-Length: 86
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip
client_id=cloud-win&grant_type=password&password=***&username=dma_k%40mail.ru
2022/10/26 10:00:44 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2022/10/26 10:00:44 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2022/10/26 10:00:44 DEBUG : HTTP RESPONSE (req 0xc00017c300)
2022/10/26 10:00:44 DEBUG : HTTP/2.0 200 OK
Content-Length: 111
Cache-Control: no-cache,no-store,must-revalidate
Content-Type: application/json;charset=UTF-8
Date: Wed, 26 Oct 2022 08:00:44 GMT
Expires: Tue, 26 Oct 2021 08:00:44 GMT
Last-Modified: Wed, 26 Oct 2022 11:00:44 GMT
Pragma: no-cache
Server: nginx
Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
X-Frame-Options: DENY
X-Host: fau27.m.smailru.net
X-Mru-Request-Id: a2427891
{"error":"invalid username or password","error_code":3,"error_description":"username or password is incorrect"}
2022/10/26 10:00:44 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2022/10/26 10:00:44 Failed to create file system for "mailru:": failed to authorize: oauth2: server response missing access_token
I tried it when found the ticket #6398, but it seems that this backend does not support reconnect.
I have created a new remote and it fails with the same error. I think I miss some details in all this story. 2FA is certainly disabled, however I have application-specific passwords (generated long time ago) – probably that started to play a role the last time.