For openSUSE Leap 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:marec2000:devel:languages:python:interpreter/openSUSE_Leap_15.5/home:marec2000:devel:languages:python:interpreter.repo
zypper refresh
zypper install python39
For openSUSE Leap 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:marec2000:devel:languages:python:interpreter/openSUSE_Leap_15.4/home:marec2000:devel:languages:python:interpreter.repo
zypper refresh
zypper install python39