It's not all that hard to imagine they make their money from subscriptions. They reached 100M accounts in 2023. Sure not all of those are paid accounts, but Proton isn't like MS or Google that offer free accounts without limits. Those limits are reached pretty quickly. They also do public fundraisers (usually around 1M) and get occassional grants from the EU. Combine that with just not so much wasteful spending as Silicon Valley and it's not that hard to imagine how they get their money. 1 billion spread out over 5 years doesn't seem that crazy to me, which is needed if the Swiss government does decide to fuck up their unique position by pass those surveillance laws. Proton's involvement in EuroStack should help too.
The real question is: if Proton increasingly depends on outside funding or strategic partnerships to chase these massive ambitions, can it really claim to be independent and safeguard user privacy, or is that just empty marketing spin?
Is that the real question though? It's based on completely unverified assumptions and speculations. Don't get me wrong. 1B is a LOT and it's totally fair to question their business model and how they make that money, but let's not get into FUD territory.