Depends. Obviously when they say “secret spyware” that means it is, in fact, secret, and we don’t know which spyware they’re using, but as the article notes it could be Paragon Solutions.
They have a system called Graphite, but that primarily targets just instant messaging platforms. If the article is to be believed when it says it could activate your camera, that would signal to me it’s more likely something from NSO Group, like their Pegasus spyware that can also access your camera, GPS coordinates, and more.
All of these are going to be reliant on zero-day exploits, essentially exploits that aren’t known to anyone yet and are still unpatched. All exploits will be a little different, but when it comes to mobile spyware, we usually see them delivered either through texts, websites, or email.
Those attacks can either be someone just receiving the text (even if they don’t click on it, AKA a “zero click” attack), or maybe having to actually go to a particular website with the exploit baked in, or running an attachment from an email.
I personally have used Proton and Tuta, and both have been pretty good to me, it just depends on what you want and how much you want to spend.
Proton is a lot more worth it if you also want additional features that would otherwise cost more to buy on their own, like cloud storage, or a VPN. (they also have a calendar, password manager, docs & sheets editing, video conferencing, and more) It also comes with unlimited email aliases if you pay for it, whereas Tuta has limits on how many aliases you can create unless you use your own domain, which then makes them much more easily fingerprintable.
Tuta is definitely cheaper though, has a much simpler and more janky UI, and has both mail and a calendar, but no cloud storage to my knowledge. They run on more green energy than Proton does, but I find they have less quality of life features than Proton. If all you need is just a cheap way to send and receive emails, with end-to-end encryption, Tuta’s definitely way cheaper than Proton and probably worth it in that case.
For Thunderbird, Tuta has add-ons to allow it to work with Thunderbird, and Proton requires a background application running to decrypt and pass along emails to Thunderbird.
Any encrypted email will require some form of add-on or bridge between them and Thunderbird since they require a way to utilize their particular form of end-to-end encryption, otherwise all your emails would appear as gibberish in Thunderbird.