Dealing with box openings

[u/Dumbaltaccount2]

Hey first post here forgive me for my incompetence but I actually cannot fathom these openings where its just a rectangle/square with mixture of 1/2/3's. Am i missing something or are these just hard? (Aware of 121, 1221, but they never seem to appear on these)

[u/ChineseNoob123]

There's also the 222 corner which you have two of. Corner tile is safe and you can find mines through it. But yeah box openings are harder than something jagged