Yes, Stellaris was appropriate a few years ago when first ported to the TI Stellaris ARM Cortex M boards, - prior to that it had been MSP430.
But, as is the nature of ARM devices, for a given core, you are dealing with a common instruction set, and the assembler and compiler tools appear to be virtually universal these days, that moving the Forth from one manufacturers device to another manufacturer seems to be relatively straightforward.
That said, the manufacturers peripherals vary considerably (notably the PIOs on the RP2040) and so the bulk of the effort in porting, will be to identify the specific peripherals and write driver code for them.
The same could be said for porting "Arduino" across a huge range of manufacturer's devices
Regarding Forth, there is also Mecrisp-Quintus, which is a complete rewrite of Stellaris for the RISC V architecture, and Mecrisp ICE which runs on a Lattice ICE 40 FPGA.
Full details here:
http://mecrisp.sourceforge.net/Incidently, Terry Porter has written a very comprehensive "unofficial" documentation for Mecrisp Stellaris, and I see that Terry has been named as assisting Matthias with the latest Stellaris port to the RP Pico.
https://mecrisp-stellaris-folkdoc.sourceforge.io/