Emscripten. If you use something like SDL porting is trivial.
Working on a project to port a 20 plus year old c/cpp code base to the web. The tooling was like 98% there but I've had to upstream a few fixes or find a workaround every now and then.
Good on you man. If I got an email that said “opportunity: port 20+ cpp app to web” I would chuckle and close that sucker real quick.
Modern cpp I maybe can deal with. That 90s stuff is real bad.