Solved: I'm not sure what exactly fixed the issue but I updated a bunch of settings. There were some Xcode warnings recommending updating project settings that auto-updated a variety of settings. I also updated the project format of each target to Xcode 12-compatible and updated the target build version to iOS 13. I also updated to Xcode 12.1 (though this alone did not fix the problem).

Update: I can run on my device but not on a simulator

I've found my issue. I think it's a new bug in watchOS6. It seems that permissions aren't being properly communicated from the handset to the watch. After giving permission for notifications on the handset, I would check for notification permissions on the watch and get .notDetermined. Strangely, if I downloaded the handset app and quickly gave notification permissions BEFORE the watch app had finished downloading, then it properly received notification permissions. I fixed this by simply requesting notification permissions on both the handset and the watch.