It’s already clear from several other question you may not maintain concentration on Mantle of Majesty and another concentration spell at the same time. This is not my question.
A creature may not normally cast 2 lvl 1+ spells in the same turn even if one is an action and the other is a bonus action. They may maintain concentration and cast a level 1+ spell that does not require concentration. They may also cast a cantrip and a level 1+ spell.
Does the “Command” free level 1 spell as a bonus action granted by Mantle of Majesty qualify as a level 1+ spell preventing the bard from casting another level 1+ spell such as “Charm Person” or “Dispel Magic” on the same turn?
I suspect it does not as most abilities such as martial moves, ki, or breath weapons are not treated as spells. However I have not found any defense for this in any of the rulebooks.