The search choice is contextual in iTunes:
If Show Apple Music Features is on in Preferences, then
- If Library is selected in the tabs on top, then the choice is between Library and Apple Music.
- If For You is selected in the tabs on top, then the choice is between Library and Apple Music.
- If Browse is selected in the tabs on top, then the choice is between Library and Apple Music.
- If Radio is selected in the tabs on top, then the choice is between Library and Apple Music.
- If Store is selected in the tabs on top, then the choice is between Library and Store.
If you are not logged in to your account, then
- If Library is selected in the tabs on top, then the choice is between Library and Store.
- If Radio is selected in the tabs on top, then the choice is between Library and Radio.