Installing Apps from other sources

Can we install GameMaker on this OS bc my son wants to make his own video game and this was his main choice to do it with.

I noticed that GameMaker only provides a .deb package for Linux, and only for the beta version, at that. Endless is Debian-based, but it is also an immutable distro, so it does not allow changes to the system.
At your own risk, you could get around this by typing a command before the classic one used to install deb files. I can’t guarantee that it will work, but the commands to use would be:
“sudo ostree admin unlock --hotfix”
“sudo dpkg -i /path/package_name.deb”