I have to MacBooks with PureOS running. On the first one I managed a setting, which allows me to switch between two keyboard settings, English and Hebrew, by pushing the command button and the space bar together. There is also a little symbol at the top of the screen, next to the wifi symbol.
On my second MacBook I am trying to do the same, but can´t get there. Only English is available for keyboard language.
Maybe you don’t get a user interface to switch languages unless two or more languages are installed. I would check whether you have installed something on the first MB that is not on the second.
edit /etc/locale.gen to enable language you are interensted.
run locale-gen
edit /etc/default/locale set locale to preffered language
edit /etc/locale.conf as above
reboot
now switch your interface language, and you shoudl be able see other keymaps