I have just the thing for you.
https://github.com/rajames440/StarForth is an ANSI C99 with minimal dependencies I wrote to port into a microkernel environment. You'll also see some inline asm for amd64 and arm64 with plans down the road for RISC-V inline asm as well. Feel free to snoop around it. The documentation is pretty good. My approach was to build it as a totally static monolithic build unlike gForth & others so it ports almost anywhere fairly easily but will still be usable as an executable on Linux without a lot of difficulty and it was designed with Ras Pi 4b in mind as well. You could clone the repo onto a Raspberian install and build it without much difficulty.