None of the standard mappers used in Game Boy/Game Boy Color games provide 32K switchable banks. They all provide a fixed 16K bank at the beginning, and a switchable 16K bank afterwards. If there are 8 bits of bank selection, the maximum cartridge size becomes 4MB, but some mappers allow more than 8 bits to select a bank.

One of the common mappers even enforces that you may not pick bank 0 for the switchable bank, picking 1 instead.

Mappers found in bootleg multicarts do allow you to change the base address and size of the game, which will move the fixed bank.