Reproduction steps:
1. Open any Unity project
2. Go Unity -> Shortcuts
3. Find Stage/Edit Prefab in Isolation
4. Try to set its shortcut to Option + P

Expected result: The shortcut is set successfully
Actual result: Binding conflict is thrown saying that P is already assigned to another function, however, the Option+P combination is not set anywhere

Reproducible with: 2019.4.25f1 (Note 3), 2020.3.6f1, 2021.1.5f1, 2021.2.0a15
Could not test with 2018.4.33f1 because there are no shortcuts settings available

Notes:
1. Unity should perceive P and Option+P as different combinations but does not
2. This does not seem to occur with all combinations the same way, and I found it hard to understand what causes this
3. In 2019.4.25f1 there is no Prefab in isolation bind, so try binding Main Menu/GameObject/3D/Quad with control + P (says that P is bound)