Technically BIP32 can act as a KDF without limit and you can derive as many keys from it as you want but if we are strictly sticking to the standard then there is kind of a hidden limit on the number of keys you can derive using this algorithm which comes from the fact that extended key encoding using Base58 (creating xprv, etc. for main master and child master keys) encodes the key depth as a single byte so it is limited to 256. Each depth uses an index which derives a different key and is a 32-bit unsigned integer ergo it can derive 4,294,967,295 keys. With 256 depth we can only derive a total of 1,099,511,627,520 keys using a single master key. This is far smaller from the number of possible private keys.

Of course we can ignore this limit easily but then it is breaking the standard and the child master keys can not be encoded/decoded using the standard.