With Safari Version 13.0 (15608.1.24.40.4) I can't install any Safari Extensions from the Safari Extensions Gallery (https://safari-extensions.apple.com). There's supposed to be an "Install" button on an extension's page, but none is visible. The only apps currently installed on this machine are Xcode, 1Password, and Slack.
I've tried changing the user agent to 10.14's but that hasn't worked.
Googling this problems shows it's happened with other OS releases, but there hasn't been any confirmed resolution to it. It's super frustrating.
Unfortunately the extensions I want aren't available in the Mac App Store, so this is the only way I can install them. Any ideas?