why don't motion 5.4 templates work with FCPX 10.3.4
Why don't motion 5.4 templates I create work with FCPX 10.3.4? I get the red screen with warning triangle.
Final Cut Pro X, Mac OS X (10.7.2)
This situation has "always" been this was since Final Cut version 10.1.0. Before that, the XML information in Motion projects did not specify a versioning. You cannot run templates in FCPX created in a newer version of Motion than older versions of FCPX (without modifications).
You really should upgrade Final Cut to the most recent version.
If for some reason you cannot upgrade now (you're in the middle of a project, don't have time, whatever), then as an alternative:
I have compiled a compatibility table:
https://fcpxtemplates.com/fcpx-motion-compatibility/#compatibilitytable
further up on the page is a method of backdating your Motion projects to make them compatible with older versions of Final Cut. You must be sure that the Motion project does not contain anything that Final Cut will not "recognize" (and there are a few additions to Motion 5.4 that weren't available in FCPX 10.3.4, like the Overshoot behavior and Fill filter). Most of everything else in Motion has not significantly changed since Motion 2, so anything that was available in Motion at the time of the FCPX version release will work. Just follow the instructions for making the modifications to the .mo⨯⨯ (xml) file.