Beyond encrypting wallet data, I don't think there is much use of encryption in Bitcoin.
Another major usage is for physical backups and cold storage where users print their keys or master keys. Those backups also must be encrypted for extra security. BIP38 comes in here but there is no standard for encrypting extended keys or mnemonics which is what nearly all wallets use these days.
BIP-39 doesn't use encryption but it specifies an optional passphrase for the key derivation.
That can't be categorized as encryption though.
Lightning uses encryption.
That is in my to-do list. Hopefully I can implement that too by the end of this year.
