Go to https://calendar.proton.me/.
Sign in to your Proton account.
In the left menu, hover over the required calendar.
Click the three dots (…) → Share.
In the Share with anyone section, set the access level to Full view.
Click Create.
Copy the generated link — it starts with
https://calendar.proton.me/api/....
Open Settings → Apps → Calendar → Calendar Accounts → Add Account → Other → Subscribed Calendar.
Paste the copied link into the Server field and tap Next.
If needed, set a description (for example, Proton Calendar) and tap Save.
Open the Calendar app — Proton events will appear automatically (sometimes with a delay).
→ Proton events will appear in the iPhone calendar list, but without the ability to edit them on the device.
Data refresh occurs with a 15–30 minute delay compared to the original Proton calendar.
Events can be managed only via the Proton Calendar web version or official Proton apps.
Settings → Apps → Calendar → Accounts → Add Account → Google.
Enter your Google account credentials and enable the Calendar toggle.
After synchronization, all calendars from your Google account will appear in the app.
→ Google events can be created, edited, and deleted directly on the iPhone — all changes sync with Google instantly.
On iPhone, both calendars can be viewed in a single app, but Proton is read-only, while Google is used for full event management.