Doing Google on catalina auto-login wifi shows a large number of entries
https://poweruser.blog/macos-catalina-wifi-issue-captive-portal-broken-45610cc016b5
https://www.igeeksblog.com/how-to-fix-wi-fi-issues-on-mac/
https://discussions.apple.com/thread/250716363
https://macreports.com/mac-catalina-wi-fi-problems-fix/
Another possibility. After attaching to the wifi server and not seeing the message, try opening the browser and going to a site such as cnn.com or apple.com. If it says something about a possibility of something impersonating the site, tell the system to ignore that for the moment. I have seen this before, and the acceptance screen will then appear and you can acknowledge there and then continue normally.
Since I can't replicate the problem on my MacBook Pro, I can't tell if this will work. However, if somebody having the problem can try this, it may be useful. It appears that the laptop is not activating the auto-login script which sends a message to captive.apple.com (to be verified). The wifi points with acceptance pages then send the acceptance page to any http request. After acceptance, the wifi access point sends the http requests to the correct server.
It is possible that the auto-login property is still attached to the wifi access point but the system preferences -> Network -> TCP-IP-> Advanced can't set the property. Try deleting the wifi service from the list on the menu generated by the Advanced button and shut down the machine. After you start up the system, see if you can get to the wifi service.