in the description at https://software.opensuse.org/package/unarj you will find 'Unarj allows for unpacking of .arj files,...'
Preliminary note: as described above, my files are self extracting archive .exe
I could find only a community package at: https://download.opensuse.org/repositories/home:/Sauerland/openSUSE_Leap_15....
package executing supplied the follwing result:
# unarj x Lager32.exe UNARJ (Demo version) 2.63 Copyright (c) 1991-2000 ARJ Software, Inc. Includes patches applied by SUSE/Novell 2003-2004.
Processing archive: Lager32.exe
Lager32.exe is not an ARJ archive #