Can't install InDesign

I'm trying to install InDesign on my second iMac (Late 2012, running Catalina 10.5.7). I have it running on my main (much newer) iMac already, along with Photoshop, Acrobat, Illustrator, etc.

I can easily enough install Creative Cloud, along with all the other apps I need, but InDesign simply doesn't appear in the list of available apps on Creative Cloud. If I go to the main InDesign webpage and click "download" there, the installer downloads, which takes me to Creative Cloud, and then.... nothing happens.

I have tried logging out and restarting, I have tried reinstalling everything, I have tried whatever the "Limited Access Repair Tool" is (I get an orange warning pop up about Limited Access), but nothing seems to work.

I feel like I'm missing something obvious, but I can't work out what is wrong!