After I upgraded to 26.7 everything worked, so I thought I was done. But when I went to enable some rules that I generally keep disabled, the rules weren't even there. Then I noticed that the interface didn't even let me select a rule (no checkboxes on the left side). I'm starting to think that I missed something big about this upgrade.
Then I noticed a Migration assistant under Firewall. Can anyone direct me to what I should do about this situation? I've read some posts about the Migration assistant, but I'm not clear whether that even applies to my situation. Thanks.
The rule UI was replaced, entirely. You need to migrate your rules to the new system. Use the migration assistant. Detailed instructions are on the migration assistant UI page. Just do as is documented there.
You might need to install the legacy rule plugin to finally delete all the legacy rules.
This was announced months ago for 26.1 - you could have gone through the migration in 26.1 already to be prepared for 26.7.