I have used proton mail for sometime but there are some very annoying features. Like if you do not login in the account for 20-30 days, email account is deactivated.
I thought this timeframe you mentioned was too short so I went to check on their support portal. Proton doesn't delete inactive accounts after 20-30 days. You would have to be inactive for one year.
If you have a Proton Account on a Free plan that has been inactive for one year (12 consecutive months) or more, your account and all data associated with it (including but not limited to emails, contacts, calendars, and files stored in the cloud) may be deleted.
https://proton.me/support/inactive-accountsThey also mention that they notify users that their Proton service will be deleted 30, 15, and 7 days before the deadline. I hope they don't send an e-mail to the account that is supposed to be deleted and that you aren't using. It would defeats the purpose informing the customers.