The Nest Protect is specifically mentioned as not being compliant, as it does not have a heat alarm module that can be used in the Kitchen. Are you suggesting just placing a regular Nest Protect in the Kitchen instead of a heat alarm (and putting up with false alarms)? I am still not convinced this would comply with the regulations, as they specifically state an interlinked heat alarm is required in the Kitchen.
I went with the FireAngel Pro Connected as I couldn’t find a better option. This is compliant with the new Scottish regulations and can be very rudimentally integrated into Home Assistant. It’s not great, but it sort of works. See here for further discussion regarding this.