Is there a value-neutral term for dressing 'modestly'?

I agree that, after protection, clothing is for signaling. I don’t think that "modest"implies a religious or belief system. To me, it means quiet, neutral, not calling attention to oneself. Neither virtuous not non-virtuous. For example, a shy person may choose to dress modestly in order to be unnoticed. Jeans and a t-shirt when others are wearing sundresses or shorts, for example. In that case, the jeans may provide a kind of psychological armor, I guess.

You may, of course, have been entirely wrong about one or both of them.

The only terms that would sound objective are those that distinguish between the clothing itself and the source of any inherent subjectivity in the description, so something like “fitting X’s idea of modesty” at one extreme, and at the other “dressed to make a bishop kick a hole in a stained glass window” or some such.

Not really relevant to the OP, but amusing true story:

We were trying to translate our restaurant workers manual into Spanish for the convenience of our cooks. One of the lines in English said, “Cooks are not allowed to wear shorts”

In Spanish, it read, “Cooks are not allowed to wear underwear.”

decorous. decorously.

Hi brossa. I don’t believe there are one-word descriptions that cover all the ways that clothing can be revealing or unrevealing. (I do think that “unrevealing” is a slightly less judgmental than “concealing.”)

Clothing can be tight or loose, heavy or diaphanous. It can be minimal (according to local laws) or elaborate. It can direct the eye toward a physical feature, or away from a physical feature. I think a writer or speaker would need more than one word to deal with all those aspects, and would need to provide the reader/listener with a little information about the social setting.

Maybe business or professional attire. As opposed to leisure/casual attire.

Business casual may be a good compromise.