Does not work on the numeric keys !!!

My standard application settings:

@leocg Unfortunately not.
The system points to Thunderbird as default mailhandler.
If I open a mailto: link in Firefox or Chromium, it opens Thundebird directly, but not in Opera !!!
There must be a big bug in the Linux version.

While trying to open Mail links, I had to realize that it's not possible.

Opera One(version: 101.0.4843.43)
Opera is up to date
Update stream:Stable
System:Ubuntu 22.04.3 LTS (x86_64; KDE)
Chromium version:115.0.5790.171

Doing the same in Chromium or Firefox opens Thunderbird as default mail program defined in Settings.
There must be a problem with Opera.
There are also no settings, to define the protocol handler.
Help is not working, because the settings described there do not exist, so help is outdated (Online Help !!!)

Has anyone a solution?
Maybe the Opera Support?

My system:
Operating System: Ubuntu Studio 22.04
KDE Plasma Version: 5.24.7
KDE Frameworks Version: 5.92.0
Qt Version: 5.15.3
Kernel Version: 6.2.0-1009-lowlatency (64-bit)
Graphics Platform: X11
Processors: 16 × 13th Gen Intel Core i7-13700K
Memory: 62.5 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 3060/PCIe/SSE2