Comment # 2 on bug 1142273 from Daniel Bauer

Sorry, I have already tried things like that, and it didn't work.

After your message I created a file ~/.Xmodmap with 1 line 
keysym Alt_R = Multi_key
and an empty line after

I created a file ~/.xsession with 1 line
xmodmap ~/.Xmodmap
and an empty line after

I rebooted. Still can't put those characters using altGr.

I only know Suse since 20 years, since 6.x, and since then until saturday
(42.3) I could always use altGr to have the Spanish ~n or �i

As you see, it doesn't work.

All these years I use Swiss keyboads of the same brand (Cherry), and with the
downgrade from 43.3 to 15.1 I haven't changed it.