You can buy SBCs that run FORTH natively. Just plug a USB cable into your computer, fire up a terminal program, and you're ready to go. It's a great way to get completely immersed in the language.
(One word of caution: Mine took several months to arrive from Australia. Look for a supplier close to you first!)
Another great way to learn FORTH is to do it like it was 1984. Load up a Commodore 64, Apple ][ or similar emulator on your modern computer, then load a FORTH language IDE into that.
The documentation of that era was written for people who were completely new to the arena, so it's tremendously easy to follow along with, and available as free scanned PDFs on the internet.
Even very cheap and readily available microcontrollers like the STM8 can be used in this way [0] [1]
I’ve found the microcontroller for less than 20 cents on Ali express, easy to solder. Add a capacitor and a TSSOP-to-DIP adapter board and you have a breakout board for less than 50 cents that can run Forth.
[0] https://github.com/TG9541/stm8ef
[1] https://hackaday.io/project/16097-eforth-for-cheap-stm8s-gad...