here is how it is done: Expertise, then use optional rules in the DMG to max out Dex to 30, then use an Epic Boon to get +10 for

No it is not. Keep in mind it is level 20. Also almost all of the rouges abilities ether work on surprised enemy's or easier to hide.

also just because they succeed the stealth roll doesn't stop anyone form looking for them

dm's guide has optional rules so that lvl 20 characters can still get more op from earning Xp.

these are mostly Feats and Ability Score Increase every [ ] XP you get.
"The ability score can exceed 20 but it can't exceed 30" is what it says.
so u can max out ur dex to 30, that gives u a +10 for dex.
Expertsise in stealth gives u a +12 at lvl 20, that so far is +22.
Then also there is a thing in DMG which is an Epic Boon which u can get at lvl 20 or lvl 10 if you have an Aberrant Dragonmark. The Boon of Undetectability (or something similar) is +10 to stealth and you cant be detected by magic. Thats +32 to stealth.

Also, i forgot what level it is but rogues have a feature where "you can treat any roll of 9 or lower as a 10" if you have proficiency or expertise. that means no nat ones, and therefore with +32 the lowest possible score is s 42 for stealth.

And it would be hard to find someone with a 42 for stealth.

But, are a class made to sneak around.

Also that doesn't stop anyone from looking for them. Also if a player dose that then the dm will just agust encounters to be more balanced. And even with all that stealth you can't hide if the enemy can easily see you.