I'm working on to create an app for Mac Catalyst platform using .NET MAUI. I'm already done with the creation of distribution certificate and provisioning profile. Also I have installed both. Now the problem is that I am unable to select the provisioning profile/certificate under Bundle Signing cause the option is grayed out.
You could create a certificate for Mac Development or Distribution on Apple Developer Portal and download it in your keychain access. I recommend this document: Provision an iOS app for app store distribution and although it's for iOS, the workflow for Mac app is similar.
Hope it works for you.