Found it : https://repo.aosc.io/debs/pool/stable/main/s/showmethekey_1.14.0-0_amd64.deb

No luck though :

$ sudo apt install ./showmethekey_1.14.0-0_amd64.deb 
[sudo] password for kaki:         
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Note, selecting 'showmethekey' instead of './showmethekey_1.14.0-0_amd64.deb'
Starting pkgProblemResolver with broken count: 1
Starting 2 pkgProblemResolver with broken count: 1
Investigating (0) showmethekey:amd64 < none -> 1.14.0 @un puN Ib >
Broken showmethekey:amd64 Depends on systemd:amd64 < 255.4-1ubuntu8.5 @ii mK > (>= 1:256.4-1)
Broken showmethekey:amd64 Depends on libadwaita:amd64 < none @un H > (>= 1.5.0)
Broken showmethekey:amd64 Depends on libevdev:amd64 < none @un H > (>= 1.11.0)
Broken showmethekey:amd64 Depends on libinput:amd64 < none @un H > (>= 1.26.2-1)
Broken showmethekey:amd64 Depends on gtk-4:amd64 < none @un H > (>= 4.14.2)
Broken showmethekey:amd64 Depends on glib:amd64 < none @un H > (>= 2.80.0-2)
Broken showmethekey:amd64 Depends on json-glib:amd64 < none @un H > (>= 1.8.0)
Broken showmethekey:amd64 Depends on cairo:amd64 < none @un H > (>= 1.18.2)
Broken showmethekey:amd64 Depends on pango:amd64 < none @un H > (>= 1.52.2)
Broken showmethekey:amd64 Depends on libxkbcommon:amd64 < none @un H > (>= 1.7.0)
Broken showmethekey:amd64 Depends on polkit:amd64 < none @un H > (>= 1:125)
Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 showmethekey : Depends: systemd (>= 1:256.4-1) but 255.4-1ubuntu8.5 is to be installed
                Depends: libadwaita (>= 1.5.0) but it is not installable
                Depends: libevdev (>= 1.11.0) but it is not installable
                Depends: libinput (>= 1.26.2-1) but it is not installable
                Depends: gtk-4 (>= 4.14.2) but it is not installable
                Depends: glib (>= 2.80.0-2) but it is not installable
                Depends: json-glib (>= 1.8.0) but it is not installable
                Depends: cairo (>= 1.18.2) but it is not installable
                Depends: pango (>= 1.52.2) but it is not installable
                Depends: libxkbcommon (>= 1.7.0) but it is not installable
                Depends: polkit (>= 1:125) but it is not installable
E: Unable to correct problems, you have held broken packages.