Bitcoin's current private key space is 2^256
Keys are chosen based on the order of the generator of the specified elliptic curve. Bitcoin uses a curve that has a G with an order that is slightly smaller than 2
256 so the space is technically smaller than 2
256.
with Bitcoin's legacy address space being 2^160 (ie. 10^47) due to its use of RipeMD160. (I have no idea about Bech32's address space though)
Bech32 (like Base58) is just a method of encoding the
same exact data that is the result of RIPEMD160 so it is limited by the same size (20 bytes hence the 2
160). In other words in legacy addresses and native SegWit (Bech32) addresses you are encoding the same thing. You can take a look at
this topic that I posted a while ago if you are interested to know how it works with an example. The steps 1, 2 and 3 are the same with Base58, Bech32 or any other future encoding we might use.