So not a complete fix yet, but one thing I've discovered is that WSL behaves slightly different than native linux (Ubuntu and Fedora)
Linux is appending 0a 07 to the output, and WSL was doing 07 "output" 0a. I was using head -c -1 to remove the trailing newline (but didn't know about the 07) so that would explain the trailing newline on TIO
Although Try it online! just appends the trailing newline (on both WSL and linux), so I'm guessing that there's an error somewhere in vim, triggering the bell, and WSl and linux handle the bell differently
Could you pull the dev version? The newline issue should be fixed, but I'm still a bit worried about the encoding. I'd like to test the program Á. in particular, which should append a "." to the input