March of the Monarchs vs Negate Tribute Summon

Question

Player A already has March of the Monarchs active on their field, which protects their tribute summoned monsters from being targeted or destroyed.

Player A attempts to tribute summon a monster face-up, but player B activates Solemn Judgement.

Question: Can player B activate Solemn Judgement?

Answer 1

Yes, Player B can activate Solemn Judgement.

Note the activation timing of Solemn Judgement (emphasis mine):

When a monster(s) would be Summoned,

I.e., the monster's summon has not been completed.

It is therefore not yet a Tribute Summoned monster, and receives no protection from March of the Monarchs.