The permissible lengths of bech32 addresses is currently laid out in
BIP173,
BIP141, and
BIP341 (links lead to relevant sections).
BIP173 states that the data being encoded must be between 2 and 40 bytes long, which once encoded along with the human readable part, separator, and witness version, gives a length of between 14 and 74 characters.
BIP141 states that for witness version 0 (native segwit), the data must be either 20 or 32 bytes long, giving addresses which are either 42 (P2WPKH) or 62 (P2WSH) characters.
BIP341 states that for witness version 1 (taproot), the data must be 32 bytes long, giving addresses of 62 characters.
So the longest bech32 address at present is 62 characters, but we currently have the option of going up to 74 characters in future versions if needed.