Use Watcom C/C++, it's freely available and fully supports protected mode extenders on MSDOS. It might be a bit dated but it works and generates pretty tight code.
Oh yes they do.
Rust is used for embedded work because (like C and unlike most languages) it is easy to arrange for the output of a Rust compiler to work without any runtime library.
https://www.indeed.com/q-Rust-Embedded-Microcontroller-jobs....
In contrast there are plenty of C/C++ compilers - but I'm not interested in those languages(boring and DJGPP[gcc/g++ for DOS) are too big for machine with 120MB of disk space).
For example NIM is "new", same with Rust.