So, I read those threads about Battle, Jousting and Parade Armor, but it didn't clarify some of the points I was expecting, or at least, how to perceive some artistic evidence showing noblemen in armor outside action situations.

Dan Howard's mentioned that Faux Brigandines, or "false brigandines", were a thing used by some wealthy people to ostentate on some occasions. The retained bodyguards of the Howard family in England was also intended to have richly decorated brigandines with silk velvet and silver/gold rivets. So, there was an idea of show-off armor, but was noblemen's brigandine only a armor for ostentation purposes?

I find this 1500-1510's painting made by the Catalan Joan Pau Guardiola, it's called "The Miracle of the Virgin of the Rosary and the Knight of Colonia" that shows a couple of knights in a sort of lighter suits of armor on a sort of church or palace environment:
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Their dresses are surprisingly similar to the sort of civilian-martial garment seen in the Portuguese Paineis de Sao Vicente, which shows armor from 1450-60's being dressed by the royal family, their noble court and some guardsmen. Besides the fact that Guardiola's and Sao Vicente are separated by almost half a century while still retaining the same armor, both of them mix a sort of civilian and lighter pieces of armor being used in non-martial context. I wonder if this was something actually common to the aristocracy of the Middle Ages to wear lighter harnesses in churches and at Court or if that's something unusual, purely personal and just an aspect of local culture. If you go to Froissart's Chronicles you often find kings wearing royal garments over armor:

King Fernando I of Portugal and King of Castile at Fernandine Wars

Famous German description of the Adoration of the Wizard Kings, showing a fully armoured man in german style and other with main and plate leggings

King Juan of Castile, at the Battle of Aljubarrota

Wat Tyler's Uprising

Afonso King of Leon and Castille

Maximilian I and his pony

So, how exactly the amount of armor or civilian garments were inteded to mix themselves at battles, at tournaments or at church/court service?

IMO in Western Europe it was pretty much all functional brigandines - even the most highly decorated ones. De Commines implies that he had never seen faux brigandine before the anecdote he recounts and seems to have been amused by it. I get the impression he considered it to be a "less than manly" thing to wear. Fully-functional, richly decorated armour was a fashionable thing to wear in court and it isn't particularly heavy. Some of the multi-layered clothing worn in court and to important functions actually weighed more than a suit of armour.

Pedro, you have some misidentifications attached to your images. Your second image is of Sabothai bringing King David water from the well near Salem, and your last image is of Charles the Bold at the Battle of Nancy. There may be others.

I don't recall any "false brigandine" in Iberian inventories I've read so far. Covered with colorful and expensive cloth, yes, dozens...

BTW, just saw the shield handle, this painting has so many details you can see new things each time you look!

Are the gentlemen in the painting simply dressed in the jinete style (or genet style, as they are Catalan), rather than fully armed men-at-arms. The armour displayed seem very functional, yet stylish. I don't think we can read this as a light or "for show" armour for church - this is I think battlefield armour for a gentleman light cavalry leader.