I have used copr to build the first alpha release of lyx-2.4:

https://copr.fedorainfracloud.org/coprs/jamatos/lyx-devel/build/1858028/ 

For EPEL7 it build for x86_64 and it fails for aarch64, due to %{python3} not being defined.

The spec file has BR: python3-devel.

In the install stage I have this:

%py_byte_compile %{python3} %{buildroot}%{_datadir}/%{name}/lyx2lyx

This fails in epel-7-aarch64:

https://download.copr.fedorainfracloud.org/results/jamatos/lyx-devel/epel-7-aarch64/01858028-lyx-devel/build.log.gz 

"

+ python_binary='%{python3}'

+ buildroot_path=/builddir/build/BUILDROOT/lyx-devel-2.4.0-0.2.alpha1.el7.aarch64/usr/share/lyx-devel/lyx2lyx

~/build/BUILDROOT/lyx-devel-2.4.0-0.2.alpha1.el7.aarch64 ~/build/BUILD/lyx-2.4.0-alpha1

+ bytecode_compilation_path=./usr/share/lyx-devel/lyx2lyx

+ failure=0

+ pushd /builddir/build/BUILDROOT/lyx-devel-2.4.0-0.2.alpha1.el7.aarch64

+ xargs -0 '%{python3}' -O -m py_compile

+ find ./usr/share/lyx-devel/lyx2lyx -type f -a -name '*.py' -print0

xargs: %{python3}: No such file or directory

+ failure=1

+ xargs -0 '%{python3}' -m py_compile

+ find ./usr/share/lyx-devel/lyx2lyx -type f -a -name '*.py' -print0

xargs: %{python3}: No such file or directory

+ failure=1

~/build/BUILD/lyx-2.4.0-alpha1

+ popd

+ test 1 -eq 0

"

while in the corresponding x86_64 the first line correctly sets:

+ python_binary=/usr/bin/python3

Is this known?

https://fedoraproject.org/wiki/User:Bkabrda/EPEL7_Python3

or

https://src.fedoraproject.org/rpms/python3-dateutil/blob/epel7/f/python3-dateutil.spec

-- 
Sérgio M. B.