How do you set up proton mail on iPad

Generally, you only need the incoming (IMAP/POP3) and outgoing (SMTP) server settings if you are manually configuring an email account. For the most part, if using the Mail Account setup wizard, your account settings are automatically detected and configured for you - and only need to provide the account Username and associated account Password:

Add an email account to your iPhone, iPad, or iPod touch - Apple Support

If you need to manually (re)configure your mail account settings, your email provider will provide details of the relevant account and server settings.

https://clean.email/blog/email-settings/protonmail-email-settings

Very often, all you need is your email address and password and the rest will be automatically populated.

Add an email account to your iPhone, iPad, or iPod touch - Apple Support

There is also a link in that article for looking up settings.