How To Have Wkhtmltopdf Working
The easiest way was to download the AlmaLinux release and then rename it to EL9: https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6.1-3/wkhtmltox-0.12.6.1-3.almalinux9.x86_64.rpm
So it looks like this: wkhtmltox-0.12.6.1-3.el9.x86_64.rpm
Then do sudo dnf localinstall ./wkhtmltox-0.12.6.1-3.el9.x86_64.rpm and then I created a test PDF with wkhtmltopdf https://apptainer.org/docs/user/latest/ test.pdf