Your system information

• Steam client version (build number or date): 0.20200113.0 (1580500660) API v020 Built Jan 31 2020
• Distribution (e.g. Ubuntu): Linux Mint 19.3 Tricia (64 bit) MATE
• Opted into Steam client beta?: [Yes/No] ja
• Have you checked for system updates?: [Yes/No] ja

Please describe your issue in as much detail as possible:

Describe what you expected should happen and what did happen. Please link any large code pastes as a Github Gist

steam game store page:
Click Demo. Downloading demo appears and installs

instead:
click Demo; nothing happens.

Steps for reproducing this issue:

1. store page
2. click demo

alternatively i have been using
steamdb "game name" demo
terminal > steam steam://install/appid#