For openSUSE Leap 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mlin7442:rebuild_fails_156:bsc1222203/openSUSE_Leap_15.6/home:mlin7442:rebuild_fails_156:bsc1222203.repo
zypper refresh
zypper install python3-sip4
For openSUSE Backports SLE-15-SP6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mlin7442:rebuild_fails_156:bsc1222203/openSUSE_Backports_SLE-15-SP6/home:mlin7442:rebuild_fails_156:bsc1222203.repo
zypper refresh
zypper install python3-sip4