It absolutely is on Larian, I'm afraid... Other games communicate the required information perfectly well and clearly, but BG3 does not. The game currently does an abominable job of explaining these things to people not familiar with D&D - and it even does a pretty decent job of actively misleading those who are. Larian often seem like they are afraid to use words, or explain things, opting for reductionist tips that are so reduced as too be inaccurate or unintelligible... and I'm not really sure why.
So the basics:
When you make an attack, whether it's a melee weapon attack, a ranged attack, or a spell attack, you are 'making an attack'; the use of the word attack is what matters here, generally speaking. In these circumstances, You roll: a d20, plus your attack modifier (proficiency bonus and the ability modifier for the attack - strength or dex for melee weapon attacks, dex for ranged weapon attacks, and your spellcasting ability (Int/Cha/Wis determined by your class) for spell attacks. No matter what sort of attack it is, you're trying to met or beat your target's AC, which is a fixed value; the enemy does not make a roll for this.
When you force a Saving Throw, mostly the purview of spells, you are making the enemy respond to your action, not making an attack. In these circumstances, Your Target rolls: a d20, plus their saving throw bonus. The type of save is determined by WHAT you are doing to them... so if you are casting a fireball, the enemy can respond by trying to leap out of the way of take cover, and so the save that they make is a Dexterity saving throw. If you try to subtly charm them or influence their behaviour, they can try to resist the odd or uncharacteristic impulses, and they make a Wisdom Saving Throw. They add the ability modifier for the type of save they're making, and their proficiency bonus if they are proficient in that type of save.
In a few select cases, a spell might make an attack roll first, and then, if it hits, compel a saving throw from the target for an additional effect; these spells are relatively few in number but they exist.
Right now, Larian's system is incapable of communicating the information it needs to without some severe revisions, unfortunately, and many folks have reported this, so cross your fingers and hope it improves with the next update to magic and spellcasting.