I create a VM with Ubuntu20.04 in VirtualBox and build inside. I have some additional "magic" to inject the build configuration into the VM and that includes a script to actually build emacs, package it as a .deb and copy that to the host once successfully generated.
For OSX, I have a script and build everything on an external disc I can plug into my different Macs to install the generated .app on them
My .2 cents,/PA
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Fragen sind nicht da um beantwortet zu werden,
Fragen sind da um gestellt zu werden
Georg Kreisler