Love Proton, DDG, and Signal. Use them all the time. Never heard of Duple. But, FWIW I use pCloud instead - it's a paid service (I bought a one-time lifetime license of 2TB of space).

pCloud's software is solid. I battle tested a number of other cloud services before selecting them. Their implementation is excellent - with virtually every other provider I found missing features or easily discovered bugs when putting them through the ringer in terms of testing.