I am having trouble installing a catalogue into 2020 version 9.1
It shows it is installed but does not show in my drop down box. Has anyone had this problem before.
Usually means that you are prohibited from using the catalogue. 2020 can restrict access to catalogues depending on license/key number.
If it's a new key, it could be set to MDV mode, or Design Essential. This cheaper, basic mode will only allow you to use very few catalogs.
If it's an existing key that suddenly changed, or if you paid for the full version of Design, simply contact Support and they'll send you an unlock code to fix your key. If you only paid for the cheapest version of Design, you may have to spend a little more to get the full version.