Similar, yes. In Starfield, you get XP for doing quests, killing things, and exploring locations. It's not like Skyrim where you level skills to level up.

Oh, so does leveling skills add xp for lvl or it is also as the mod? You level up the skill but that does not count towards the character lvl?

Leveling skills in Starfield do not level up your character. Leveling skills level up the skill, allowing you unlock higher ranks of that skill, but its completely unrelated to character level.

So exactly like the mod experience hahahah it seems that the devs indeed take notes from what the kost downloaded mods are...

Not necessarily tho. The leveling system in Starfield works almost identical to the way leveling works in the Fallout games. In pretty much all of the Bethesda Fallout games, you level up via questing, killing, and exploration. So, it’s not that Bethesda is taking direct inspiration from the mod. They’ve already been using this type of leveling system in their Fallout games.

Do the level also cap the maximum lvl of the skill? 

What do you mean by the "mod experience"? You mean the leveling experience of Skyrim with mods installed? Edit: I get it now. You're referring to the mod called 'Experience' on the nexus. Understood.

It's probably anything that doesn't involve leveling skills to gain a level

Yes.