On old mame pages I found that the tapes with BASIC would be supported, yet they don't load in 265 or 266.
BASICs are respectively mz1z001 and mz1z002.
Could also be that some tape games need these BASICs to work.
You are able to find manuals but they are all in Japanese but it gives an impression.
There seem to be better emulators and and also some info can be found on websites containing sharpmz in the address.
Though it's quite difficult to know what all commands do inside tf-dos and in BASIC should that work.
However BASIC seems to be from Microsoft so I think it has a lot of similarities.
Found that you can type HELP in tf-dos to find the commands.
You can use DIR to list the files.