In x16emu from snap this gives 255=$FF:
PRINT PEEK($FF80)
I would suggest you take rom.bin from the officially released archive for Windows, because this ROM should work if you compile the released source. This way more programs will work that check the Kernal version. During development of the ROM there are some application developers that make programs that work with some later versions of the ROM and use detection of ROM version.
"The KERNAL version can be read from location $FF80 in ROM. A value of $FF indicates a custom build. All other values encode the build number. Positive numbers are release versions ($02 = release version 2), two's complement negative numbers are prerelease versions ($FE = $100 - 2 = prerelease version 2)." - https://github.com/commanderx16/x16-docs/blob/master/Commander%20X16%20Programmer's%20Reference%20Guide.md
In x16emu from snap this gives 255=$FF:
PRINT PEEK($FF80)I would suggest you take rom.bin from the officially released archive for Windows, because this ROM should work if you compile the released source. This way more programs will work that check the Kernal version. During development of the ROM there are some application developers that make programs that work with some later versions of the ROM and use detection of ROM version.