Correct. He's looking for a CLIENT software, not a provider.
BTW I had (well, technically still have) a Proton account, but I cannot access it anymore since they revised the user interface and failed to consider that some of us still run laptops with the last STABLE operating system i.e. Windows XP. They were monumentally arrogant about it, too, as only the Swiss can be.
I'm still running Thunderbird. Have pretty near 20 years of email history archived in it, and won't change until you pry my laptop from my cold, dead hands.
ProtonMail has a limited free service, but to get the full benefit you will also pay a monthly fee.