How do you actually handle communications you really don’t want subpoenaed?

Genuine question for the lawyers here, especially anyone doing federal defense or sensitive corporate work.
When you have a client communication that absolutely cannot end up in discovery or in front of a grand jury, what do you actually use? Signal with disappearing messages? Some custom setup? Just stick to phone calls and in-person?
I keep reading think pieces about “harvest now, decrypt later” — the idea that encrypted stuff intercepted today gets decrypted in 10 years when computing catches up. Is this something you actually think about for your practice, or does it feel theoretical?
Also curious whether any of you have had clients ask for something more bulletproof than Signal, and what you told them.
Not selling anything, not a vendor, just trying to understand if this is a real concern in practice or just something tech people worry about.
Thanks.