If you're installing that RPM (which I'll note is an old version - you should use v5.4), you're presumably using CentOS/RHEL 7.x. On that platform, the python3 package is v3.6.8, not v3.9.6 which begs the question; how did you install Python 3? If you did not do so using the vendor supplied packages, then installing pgAdmin won't work, and it most likely won't work even if you forced the installation.