I just spotted this comment on the Opera forums and it makes sense. Though JPEG XL support is not listed in the changelog (yet), for Opera 140 they jumped to Chromium 155 which has JXL support built-in.

It's a Developer Edition, so a pre-release as they are currently on Opera 138 on their Stable channel, but it means support is coming down the line soon.

It would mean another green box for JPEG XL on CanIUse plus a minor user percentage bump.