Hello,
I am using iRedMail on CentOS Stream 8 in its latest version, with SoGo version 5.12.1 (root@202505160512).
When I create an entry from Outlook 2021, everything works as expected, and the Sogo logs contain these lines for each new entry:

May 30 09:25:06 sogod [2291864]: redmail01.mail.dragon-cloud.org "POST /SOGo/Microsoft-Server-ActiveSync?Cmd=Sync&User=gallina.lukas@luckypoint.cz&DeviceId=8A0DD9F2C86C4F6B94B531944BAEF6E2&DeviceType=WindowsOutlook15 HTTP/1.0" 200 143/619 0.074 - - 0 - 26

May 30 09:25:06 sogod [2291864]: redmail01.mail.dragon-cloud.org "POST /SOGo/Microsoft-Server-ActiveSync?Cmd=Sync&User=gallina.lukas@luckypoint.cz&DeviceId=8A0DD9F2C86C4F6B94B531944BAEF6E2&DeviceType=WindowsOutlook15 HTTP/1.0" 200 494/712 0.096 - - 0 - 26

However, when I create an entry from Outlook 365 (tested version 2504, build 18730.20186), the log contains fewer details:

May 30 09:32:53 sogod [2293550]: redmail01.mail.dragon-cloud.org "POST /SOGo/Microsoft-Server-ActiveSync?Cmd=Sync&User=gallina.lukas@luckypoint.cz&DeviceId=1CA01CD6A19B48789BFA9300FA70D26A&DeviceType=WindowsOutlook15 HTTP/1.0" 200 0/712 0.108 - - 0 - 14

…and the entry is not inserted into SoGo. Other actions such as editing or deleting records work fine; only the creation of new entries for synchronization does not function properly.
As a temporary workaround, we are currently using web access to SoGo, and entries created through the web interface work correctly.
Thanks!
Let me know if you'd like any refinements!