German ß can't be inserted with compose key

[oz123]

Expected behavior

I configured the compose key to be AltGr on my laptop, using mate 1.22.1.

These should work.

compose key + " + ss = ß
or
compose key + ss = ß

Actual behavior

All these work
compose key + " + A = Ä

compose key + " + O = Ö

compose key + " + U = Ü

Typing the combinations specified in above does not enter ß.

Steps to reproduce the behavior

Install mate desktop 1.22.1 set compose key and try to enter the key combinations.

MATE general version

1.22

Package version

1.22.1

Linux Distribution

Gentoo.