please replace from

source=(${_pkgname}::git+https://github.com/violetumleditor/violetumleditor.git)
sha256sums=('SKIP')
_release_commit='495649c5798d207de3410ceacca3eb0221fc4e6f'

to

_release_commit='495649c5798d207de3410ceacca3eb0221fc4e6f'
source=(${_pkgname}::git+https://github.com/violetumleditor/violetumleditor.git#commit=${_release_commit})
sha256sums=('SKIP')

otherwise commit version and pkgver are not match

or change pkgver function...

It does not build due to a misnamed violetumleditor deb package ('violetumleditor-2.5.3.deb'). It should be "violetumleditor-${pkgver%%+*}.deb" so that the right package version is used to look for this file.

So:

bsdtar -x -f ${srcdir}/${_pkgname}/violetproduct-deb/target/violetumleditor-2.5.3.deb -C ${srcdir}

should be:

bsdtar -x -f ${srcdir}/${_pkgname}/violetproduct-deb/target/violetumleditor-${pkgver%%+*}.deb -C ${srcdir}