Match the channel to the sensitivity
Most data leaks are not dramatic hacks. They are ordinary messages sent through ordinary channels that happened to keep a copy. Email archives, chat sync, notification previews, and cloud backups all preserve sensitive text long after both parties have forgotten the exchange.
The first rule of sending sensitive information online is simple: assume every plaintext channel retains what you send. Once you accept that, the solution becomes obvious. Encrypt before sending so the retained copies contain nothing readable.
A workflow you can repeat
Paste the sensitive details into Secure Notes, which encrypts them in your browser with AES-256-GCM before upload. Set an expiration that matches how long the information is actually useful, then send the link through your normal channel.
For anything especially sensitive, split the delivery: link through email or chat, decryption password through SMS or a phone call. If the recipient only needs the information once, choose burn-after-read so the ciphertext is deleted at first view. The whole flow takes about a minute and leaves no readable trail behind.