Update required for Numbers

Current config:

Numbers will not let me use shared spreadsheets on desktop without upgrading macOS.

Current Numbers upgrade is incompatible with Mojave, minimum 10.15 required.

Work IT has forbidden update to Big Sur.

Hence need to to upgrade from Mojave to Catalina.

This link opens Catalina page in App Store:

When I click on "Get" it takes me to:

Which takes me nowhere.

I could really do without having burned 2 hours this morning trying to resolve.

Help appreciated in the full knowledge that it's peer to peer, and that expecting support from Apple directly is too much to ask.