What are the chances of accidentally sending satoshis to an incorrect (but in use) BTC address, if a single character is mistyped in a Bech32 (SegWit) address?
The chance is very small if it is bech32 address. You will see the address not valid in nearly all cases.
bitcoin address are a pubkeyHash encoded in base58 with something called a checksum and version value
This isore about legacy addresses. Base58 addresses are the P2PKH and P2SH. OP is asking about Bech32 and you are right about it. Bech32 is more advanced in checksum than base58, which means the chance sending to write address because if type is significantly lower than in base58 addresses.