NOTE: I prefer to save these keys in plain text because if I die or get a serious brain injury, I want my family to be able to get the coins instead of burying them with my "brain wallet" or secret password.
I thought a lot about encryption and inheritance, not just encryption of BTC wallets, but also just general files, fotos, letters.
I have been using full disk encryption for a long time and also thought about ways to securely convey secret messages to family in case I die.
You could check if it is possible in your jurisdiction to leave behind with a lawfirm / notary a sealed letter that is only to be opened privately by your family or a specific family member.
It could contain just the passphrase to your encrypted volume, possibly contact details of a friend who can help family with decryption if needed.
The friend and your family could be told about this in advance. The passphrase could also be used to decrypt a password keeping software that contains other passwords that you would them to have access to.