Steps to reproduce:

1. Create a new project with Unity 2020.2
2. Switch to iOS
3. Go to player settings, locate 'Bundle Identifier' field
4. Notice it's now greyed out by default and is generated out of 'Company Name' and 'Product Name' fields
5. Toggle 'Override Default Bundle Identifier' checkbox
6. Change the bundle ID to something else
7. Make an iOS build
8. Open Xcode project

Expected result: Bundle ID in 'Signing & Capabilities' tab should be set to whatever you entered in step 6
Actual result: Bundle ID is still the same as the default one generated from Company & Product names

To add to that, 'Bundle Identifier' field works even worse when upgrading a project from older Unity versions - bundle ID always stays set to whatever was set in the previous version, you can't change it via current editor at all.

Reproduced with: 2020.2.0b5, 2020.2.0b7, 2021.1.0a1
Not reproducible with: 2019.4.11f1, 2020.1.0b1