On https://www.inwx.de, Enpass is unable to fill out the form hidden behind the login button in the top right corner and it does not offer to save a Webform either. The element IDs in question are "usern" and "pword". I also tried Bitwarden, which had no trouble filling out those fields. There is another, dedicated login page at https://www.inwx.de/customer/login, which is fully compatible with Enpass, despite using the same ID and name for its fields.
This occurred on both Windows 10 and Fedora 33 with Firefox 85.0.1.