Program to open .mtb file

All the documentation for regina-rexx has a file extension of mtb. Is there an application on openSuSe to open a file with an mtb extension?

May you explain what documentation you mean? Because the documentation contained in the official Regina-REXX-doc-3.9.1-bp154.2.57.x86_64.rpm for Leap 15.4 are pdf?!
The mtb files are not documentation but they are binary files which contain native language error messages. See chapter 10.2.1:

My apologies. I was looking in the wrong place. I was looking in /usr/share/Regina-REXX instead of /user/share/doc/packages/