What is the highest possible damage you can do with a level 20 character

Let’s say no multiclassing aloud and no magic items. For this we also can say that you are just going to take the average of all damage. Next, this is an AC 20 monster and has 20 in all stats (which is absurd I know, but just go with it.)It also has proficiency in strength and dexterity saving throws. The proficiency for this monster is a +5. Also, we can say you have 1 prep round before battle, then you have to try to do as much damage as you can in one round. Also, there would be no other people in your party, it would just be you. For the Wild Magic Table for Sorcerers, we can say that you can pick what you get on the table which means it is fine if you have slightly ideal damage there. Although for any damage rolls, we can say it is average damage. For this, you would use an average roll which would be 10ish on a d20. Also we can say that with saving throws, the monster rolls a 10 and then adds all of its modifiers and proficiency bonuses if any in that saving throw. Lastly, it is not allowed to do polymorph then power word kill.