When trying to create firewall shaper rules. The UI will not allow entering of port ranges for _dst-port_ or _src-port_ fields. Please see example marked up screen capture.

I'm seeing this same behavior, was trying to set up a rule to prioritize mosh traffic, which uses a range of UDP ports.
I think this worked by accident a long time ago, our port validator seems to be missing support for ranges. I'll put it on my list.
https://github.com/opnsense/core/commit/0f6b29f5bbe15e7bf3b2e276f36e4921626d2e1e should do the trick
Do I test this patch by running the dev branch or can I test this patch using production 18.7.10_3-amd64?
I think it fits 18.7 too, we'er very busy with 19.1 at the moment, so you have to test for yourself to be sure.
Is there no way to use an alias for these fields? That, comma separated, or by using tab as shown here?

The image shows a list of non-contiguous ports that I'm trying to use in two separate traffic shaper rules, and I just updated to 20.1.3 from 19.7.8 in hopes of fixing this. In _both_ releases, I can only enter one range. It will accept one port at a time, or a single range, but not a combination. I tried the same in Src-port just to test and it's the same result.
I even tried manually downloading
PortField.php
and
TrafficShaper.xml
and updating them in their respective folders via ssh, but the issue persists.
Is there something I'm missing? Has anyone else been able to use aliases or more than one range per rule?