I think he meant to say “8-bit board”.
Thermal runaway is merely a software subroutine that checks if heat was applied and if the temperature is increasing. If heat was not applied and the temperature is increasing, you have a problem, so shut down the printer. It’s not a difficult concept to program in, so just about any firmware could be modified to include it if the developers of the firmware thought of it.
The only limitation is the memory on the controller board. Obviously any additional programming loops require additional memory, but thermal runaway is fairly minimal in its most basic form.
I agree with @Jason, that you shouldn’t entertain running a remote printer without it.
So, check your board revision number, get the latest firmware for it and read up on what features it comes with.
Obviously, you have to weigh the value of whatever project you’re working on against the cost of buying a new board primarily just to print it, but also keep in mind that a modern, full-featured board, which may be overkill for an Ender3, can be used later to upgrade another printer, if applicable, so in that sense, it may be worth spending the money just to have up-to-date parts.