If you really want to play this mod then there is something you can do:
Go to Steam library, right click on Mount & Blade Bannerlord, click properties, click betas, select the beta you would like either 1.1.5 or 1.2.0 and then it will download that beta.
You can download Tetsojin mod for 1.1.5 or 1.2.0 here: https://www.nexusmods.com/mountandblade2bannerlord/mods/2564?tab=files
Then simply put the file in "modules" in Bannerlord folder and enjoy the mod.
As much as I know developer of this mod is working for a company and doesn't have time to update the mod for now.