### Description RHEL8 and rebuilders (Oracle Linux, AlmaLinux, Rocky Linux et al) now include Python 3.9 in base system.
This RFE is for ≥ 5.6.x: can we switch the `app_python3` package to use the Python 3.9 packages - no external repos will be required for switch.
This will allow newer Python 3.9 features in the routing script and keep up to date with improvements in the Python language.
Further more Python 3.6 is EoL on 23 Dec 2021.
I don't propose this for 5.5.x as it may be too intrusive but perhaps the switch could be made on master in anticipation for 5.6.x.
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### Expected behavior `app_python3` module will now use system Python 3.9 packages instead of Python 3.6 packages
#### Actual observed behavior `app_python3` module in 5.5.x now uses system Python 3.6.