Counterspelling or legendarily resisting a Critical hit spell attack [closed]

I was wondering:

  1. ABOUT COUNTER SPELL if my sorcerer casts a spell Rolling 20 against a magic user (normal npc or a boss), Can they counterspell it?

Or is this dependent on the DM’s house rules?

Let’s say my sorcerer is critting with a lvl 6 chain lightning against a lich. Would it be possible for The lich to just counterspell and on a success rob my character of the sweeet sweet taste of satisfaction, as the air starts smelling of crispy lich and singed phylactery?

  1. ABOUT LEGENDARY RESISTANCE Legendary resistance is about saving throws, not about whether my sorcerer’s spell attack is higher than the enemy’s AC… But if my sorcerer crits with a spell (that has a spell save) against a boss that has legendary resistance, can that boss still choose to just succeed their save? … or is this depending on the DM’s rules?

Let’s say it’s a dragon. It still has at least one legendary resistance left, and my sorcerer crits using a disintegrate. The spell attack is higher than thedragon’s AC – the spell hits…

But a successfull dex save means no damage. But as it’s a crit… would the boss get to use the resistance? If a 20 means a guarantied hit, it shouldn’t get the spell save… right?

If my sorcerer has both disintegrate and chain lightning, and the boss hasn’t spent all legendary resistances, then it would be better to use the chain lightning, because a successful save would still result in SOME damage.

Hope some of you can help me 🙂

Best regards Christina