So I don't really want to create a whole new topic for this, but I am having the same issue.

The spellchecker works, just there is no auto correction or correct spelling suggestions when using Outlook via Opera web browser.

Opera One(version: 100.0.4815.76)

Update stream: Stable
System: Windows 10 64-bit
Chromium version: 114.0.5735.199

Any idea for a fix?