N1b can I ask how much you pay for 2 years of Proton Duo? I wasn't aware they sold 2 year plans of it. I currently see 14.99/month for 1 year.
Regarding the alternatives, they're not strictly better. For example:
Tuta does not provide IMAP support at all whereas Proton supports IMAP on desktop. Unless things have changed recently, importing emails is either impossible or limited and exporting emails isn't great either. I've heard their search feature is even worse than Proton's. Tuta does encrypt more parts of an email, but this still requires both sender/recipient to be using Tuta.
Mullvad VPN is more often banned, has far fewer servers, is very slow for torrenting, and doesn't work well for things like torrenting and streaming. It's more of a niche VPN for ultra privacy/security people in my opinion whereas Proton is still very private and secure for 99.99â„… of people while still providing casual features like streaming support, faster speeds, and usability.
Duck.AI is still just a proxy, as you say, so it's unclear how much you should really trust it. And similar to other DuckDuckGo services, it's not open source.
Tresorit isn't open source. Frankly, the best solution is to either self-encrypt your files using tools like Cryptomator or rclone, or self-host on a server you own. The major issue with this strategy is that Cryptomator/rclone don't work well for things you want to view/edit on the cloud without downloading, such as photos/videos and online document collaboration. If you're not self-hosting, then Ente Photos for photos/videos and Cryptpad for office collaboration. Though unless you need real time collaboration, syncing office documents using Cryptomator and working offline is easy enough since these files are small.