warning: 'retain (or strong)' attribute on property 'window' does not match the property inherited from 'UIApplicationDelegate' [-Wproperty-attribute-mismatch] [/Users/user/Projects/cds-tims-mobile-client/TIMS.csproj]

but the app never actual built or ran on my phone. Every subsequent time I have tried running it on the phone I get the exact same error as my above app

You can report your situation on this issue: warning "retain (or strong)' attribute on property ... #10722, or create a new issue for it on MAUI GitHub issue. Let our developers know and deal with it.