TL;DR: the root cause for this is that not enough people are using the latest versions, see below for details.
While this is a bug, it's not directly on SE side this time. They read the data for the browser support page from an external source, which is the data behind caniuse.com, and as you can see there, the Opera version is indeed outdated while other browsers appear to be fine.
After some digging, looks like I found the reason: not enough people use the latest versions of Opera, so it falls below that site's radar, so to speak. See here under "Browsers not included on site":
The following tables display the browsers logged by StatCounter that are not accounted for on the caniuse.com website.
And the table indeed showing Opera 104.0
with only 0.009% users. 105 isn't even showing meaning less than 0.001% of the people monitored by StatCounter are using the latest version of Opera.
So while technically a bug, fixing it would require either manual update by SE itself which isn't feasible, or finding a more reliable source, which update in some other way, not based on user stats.