Currently, when i need to access my customer's PayPal merchant account (to manage IPNs or to update notifications preferences for examples), i login to the account using his credentials and his 2FA (asking him the SMS code).
Is there a feature similar to Stripe Team which allows team members to access a PayPal merchant dashboard with their own credentials? Right here i am talking about the account dashboard, not the developer dashboard, but my question applies to both!
All of this doesn't seem very efficient and secure, is there another way?
Am i supposed to use my credentials only to develop the website (on developer.paypal.com) and never connect to the actual merchant's PayPal account? And ask the customer to do every manipulation on his account himself telling him the way?
Typically you should only need to obtain API credentials to integrate with, which for current solutions are in the developer dashboard. Other account settings and operations in the account are not something web developers need access to, other than maybe some initial setup tweaks to the website preferences page. To the extent other settings matter, it is likely you are making wrong integration choices or using old legacy PayPal products (not good--for instance, you tagged the above with IPN -- what year is it? why would you be using IPN in 2023?)
Anyway, it is possible to create and manage user access within a PayPal account. This is usually only used for in-house staff, not a vendor/contractor since you should not need it, but in theory it can be used for what you're asking.