Sometimes you need to share passphrases and files – it’s hard at the best of times and in an incident it can be really difficult.
These two are really easy to use and together you can send a passphrase and then a file encrypted with that received passphrase.
The beauty of the https://onetimesecret.com/ site is you can share a password with someone and if they can see the passphrase you know they got it. If they get an error you know it was compromised en-route.
Once they remote person has a secure passphrase you can then use it to encrypt the file to send and you can use something like https://wormhole.app/ to share it over HTTPS.
See both are easy to use and default to secure mode. Remember however, that one person’s secure file sharing is another persons exfiltration tool, so you might want to ensure you track and alert on the use of these tools.