Here are some instructions from March 2020 on how to install Zoom from the Chrome Web Store onto your Chromebook –

For some odd reason, the Chromebook we tried installing the extension didn’t click-thru to the right link when trying to join a zoom meeting. So with some effort, finally found the direct link to the Zoom extension in the chrome web store.

What does show up easily on the store is this Zoom Scheduler extension in the chrome web store:

Maybe the recent surge of interest in Zoom caused a server issue-