This is a spin-off & more in-depth idea (at least in my opinion) of this suggestion:
https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/48528431-all-in-one-desktop-app
I was a bit confused on what exactly was wanted, but here is what I am looking for and hope many others will agree or add onto this suggestion.

What is this looking to solve?

Currently as it stands, proton users must navigate several pages or find the https://protonapps.com/ site, which still may direct users to web pages or wiki pages on the install process (e.g. Linux - Proton VPN). There is no easy central way to download applications, which may not seem as an issue to some, but it can be seen as an opportunity to expand and centralize the applications, if users wish to do so. This would not replace the current installers, but rather be an opt-in app management & access solution. Think adobe/m365, but not **** & 1000x better.

What would it support?

Simply every operating system/distribution will have its own primary installer (MacOS, Windows, & Linux) (Maybe android/apple devices as well). More specifically for Linux, you would be able to choose whether it is a native install (apt/rpm) or via flatpaks (proton would need official flatpaks at that time (kinda wanting this too for image based os).

Besides that, you would be able to pick and choose which applications you want to install; you could choose the whole suite or a single application. It would check updates on startup, show release notes, etc. You can also access everything through it, similar to how on the web there is the apps icon, but instead of opening a new tab, the whole application swaps over to the chosen app.

Personally, I have all my stuff with proton with a custom domain. Something like this would be a great QoL feature, & opens the gateway to better application support with flatpaks, better apt/rpm support, & other OS specific funsies.