Do you need to strengthen a mitre joint

[marcros]

Rebate the top to accommodate the sides and if necessary add a mitred face frame?

 

[ScaredyCat]

How about mitred box joints?

https://www.finewoodworking.com/2017/12/07/make-mitered-finger-joints
.

 

[Adam9453]

Loose tongue joint to strengthen the mitres and stopped housing joint for the shelf to avoid it showing as housed at the face. Or cheat and make it however you like then veneer the face edges last to give the mitred appearance