Testing of:

   0001-Use-PYTHON-variable-detected-in-configure-in-guicast.patch

And on top of that:

   0005-Add-python3.12-python3.9-to-configure.ac-check-use-i.patch

Result is acceptable to me but on Fedora 42 with python3 link to python3.13 AND NO python itself (which was a contrived test when I temporarily renamed the python file to temp_python), I get the following:

checking for gettext... gettext
checking for libtool... $(SHELL) $(top_builddir)/libtool
checking for python3... python3
checking for gtk_init in -lm... yes
checking for nasm... yes

...

  using: with-booby = yes
  using: with-clang = no
  using: python = python3

...

autoreconf: export WARNINGS=
echo >> build/config.h "#define ARCH_AARCH64 0"
autoreconf: export WARNINGS=
make[3]: Entering directory '/tmp/cinelerra-5.1/thirdparty/djbfft-0.76'
( cat warn-auto.sh; \
echo CC=\'`head -1 conf-cc`\'; \
echo LD=\'`head -1 conf-ld`\'; \
cat find-systype.sh; \
) | sh > systype
patching file configure.ac
Hunk #1 succeeded at 879 (offset 6 lines).
env: ‘python’: No such file or directory
autoreconf: Entering directory '.'
touch /tmp/cinelerra-5.1/thirdparty/../thirdparty/build/tiff.source
autoreconf: configure.ac: not using Gettext
env: ‘python’: No such file or directory
autoreconf: Entering directory '.'
CONFIGURING lame

I will send the whole log just to you.