[RPG] Can the Raulothim’s Psychic Lance spell hit a creature behind full cover if you utter the creature’s name

1. No, you cannot target a point that is blocked by total cover.

From Players Handbook, Spellcasting, subsection "Targets":

To target something, you must have a clear path to it, so it can’t be behind total cover.

If you place an area of effect at a point that you can’t see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.

When you cast an area spell, you can place its point of origin on your side of a wall, but not on the opposite side of the wall.

2. No, area effects normally do not go around corners (unless the spell explicitly says it does).

From Players Handbook, Spellcasting, subsection "Areas of Effect":

A spell’s effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn’t included in the spell’s area. To block one of these imaginary lines, an obstruction must provide total cover.

Lets say you cast Spike Growth and put its point of origin near a wall, at a location that isn't behind total cover. The spell's radius would extend in all directions from its point of origin, but it would stop at the wall. The ground behind the wall would be unaffected.

This is the cast for most spells. However, there are exceptions (such as Fireball) that specifically mention going around corners. In those cases, the spell's text overrides the general rule for other spells, and so that spell's effects will not necessarily stop at a corner.

Your conclusion is correct.

If the Cover's AC is too great, then it won't be possible to hit the Cover incidentally while trying to attack the covered creature. Either you'll roll high enough to hit the Covered Creature, or you'll roll just barely low enough that it'll miss both. In that situation, if you wanted the cover to take damage, you should be targeting it directly.

The rule is mostly designed to handle objects like Walls, where their AC is usually pretty low and intended to crumble + break when used as cover. Obviously, it applies to creatures as well, which means a lot of high AC creatures straight-up cannot be hit if they're not being directly targeted, but that generally makes sense: if a covered creature has an AC of 12+2==14, and gets missed by a 13, you wouldn't expect that to target the Covering Creature with an AC of 20, since that would lead to that creature being inexplicably easier to target just because they have an object behind them. That doesn't make much sense.