I will have to retype everything again—darn, my first message was deleted because I included some relevant links
I built FreeBASIC from source and was able to compile Basic programs just fine but the produced executables won't run, they give this error
GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._g_2dexec_2derror_2dquark.Code8

the FreeBASIC wiki describes how to bootstrap FreeBASIC