Hi,
I confirm the issue using SOGo web client.
By defining a reminder in the event, the .ics file attached to the email sent by SOGo appears "corrupted". Unfortunately, it is not possible from Outlook or Outlook Web to insert it into the calendar and manage it directly from the email.
Everything is ok without reminder, as previously said.

Hello,
I've just test it between Outlook and native SOGo and it works fine. COuld you give the "corrupted" .ics file?

I would like to refresh this ticket because I encounter the same situation(version 5.11.2 and 5.12.0)

When event is created from SOGo webmail with enabled "reminder" option, Outlook(Microsoft Outlook® for Microsoft 365 MSO (version 2412 16.0.18324.20272) 64-bit)
display it as unsupported. The same with web access(outlook.office.com).

What I have found seems to be related with VALARM block placed in the middle of the .ics file.
When it is placed at the end, Outlook imports event correctly.
I tested it manually by editing the .ics file and moving VALARM block to the end.

What is strange, saving this "unsupported" ics file to the disk then importing it manually into Outlook(File > Open & Export > Import/Export. In Import and Export Wizard box, select Import an iCalendar (.ics) or vCalendar file (.vcs)) works just fine.

https://answers.microsoft.com/en-us/outlook_com/forum/all/ics-import-file-outlook-not-dealing-with-reminders/ffdcd5d8-9d27-4c0f-867c-f8044806843c

If I should open a new ticket, please let me know.