[Bug]: `Parse error: Invalid Mimedir file`

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When ai try to accept some events(mostly coming from Outlook) i get an error and i can't accept it.
logs shows:
"This resource only supports valid iCalendar 2.0 data. Parse error: Invalid Mimedir file. Line starting at 40 did not follow iCalendar/vCard conventions"

Steps to reproduce

1.Someone with outlook send a meeting
2.I try to accept with Thunderbid and fails

Expected behavior

Accept the meet and see it in the NC calendar.

Installation method

Community Manual installation with Archive

Nextcloud Server version

28

Operating system

Debian/Ubuntu

Nextcloud Logs

{"reqId":"ANScfS8F8UcrDZFDrIHM","level":3,"time":"2024-05-29T19:26:31+00:00","remoteAddr":"172.x.x.x","user":"admin","app":"webdav","method":"PUT","url":"/remote.php/dav/calendars/admin/personal/XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX.ics","message":"This resource only supports valid iCalendar 2.0 data. Parse error: Invalid Mimedir file. Line starting at 40 did not follow iCalendar/vCard conventions","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:115.0) Gecko/20100101 Thunderbird/115.10.1","version":"28.0.6.1","exception":{"Exception":"Sabre\\DAV\\Exception\\UnsupportedMediaType","Message":"This resource only supports valid iCalendar 2.0 data. Parse error: Invalid Mimedir file. Line starting at 40 did not follow iCalendar/vCard conventions","Code":0,"Trace":[{"file":"/var/www/nextcloud/3rdparty/sabre/dav/lib/CalDAV/Plugin.php","line":766,"function":"validateICalendar","class":"Sabre\\CalDAV\\Plugin","type":"->"},{"file":"/var/www/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"beforeCreateFile","class":"Sabre\\CalDAV\\Plugin","type":"->"},{"file":"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":1094,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php","line":504,"function":"createFile","class":"Sabre\\DAV\\Server","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"httpPut","class":"Sabre\\DAV\\CorePlugin","type":"->"},{"file":"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":472,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":253,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":321,"function":"start","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/nextcloud/apps/dav/lib/Server.php","line":373,"function":"exec","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/var/www/nextcloud/apps/dav/appinfo/v2/remote.php","line":35,"function":"exec","class":"OCA\\DAV\\Server","type":"->"},{"file":"/var/www/nextcloud/remote.php","line":172,"args":["/var/www/nextcloud/apps/dav/appinfo/v2/remote.php"],"function":"require_once"}],"File":"/var/www/nextcloud/3rdparty/sabre/dav/lib/CalDAV/Plugin.php","Line":806,"message":"This resource only supports valid iCalendar 2.0 data. Parse error: Invalid Mimedir file. Line starting at 40 did not follow iCalendar/vCard conventions","exception":{},"CustomMessage":"This resource only supports valid iCalendar 2.0 data. Parse error: Invalid Mimedir file. Line starting at 40 did not follow iCalendar/vCard conventions"}}

Additional info

This happens for example when the ICS file have an "_" in some parameter most of the time is: X-ENTOURAGE_UUID
I found this closed thread but still happens: https://github.com/nextcloud/server/issues/16679

Start with the validation path in 3rdparty/sabre/dav/lib/CalDAV/Plugin.php, especially validateICalendar, and the DAV entry points named in the trace. Reproduce the failure with an Outlook-generated ICS file containing the reported X-ENTOURAGE_UUID parameter and inspect line 40. Done means the meeting can be accepted through Thunderbird and appears in the Nextcloud calendar without the invalid Mimedir error.