If macOS 10.15 Catalina (and also 10.15.1, unfortunately) broke your ability to connect to certain Wi-Fi access points because the captive portal (splash page) does not appear, manually launching /System/Library/CoreServices/Captive Network Assistant seems to help. Thanks https://poweruser.blog/macos-catalina-wifi-issue-captive-portal-broken-45610cc016b5 for the suggestion!