Yes - that may happen - such packages are the local system administrators job to keep working.
Openshot depends on qt5 libraries which are no longer available in the official repository - and may prove difficult to get working.
Again - custom packages may fail when the expected dependencies no longer exist.
AUR is Arch User Repsotory - it is expected that those build scripts may fail on Manjaro due to either unresolved dependencies or system libraries being an unexpected version.