Hello machepap,
If you haven't already done so, let's use the steps below to check for those credentials is the Safari Settings or Preferences:
1. Open Safari.
2. From the Safari menu, choose Settings (or Preferences), then click Passwords.
3. Sign in with Touch ID, or enter your user account password.
4. Select a website.
You can also find those steps in this resource: How to find saved passwords and passkeys on your Mac - Apple Support
If your credentials still aren't showing up there, do you sync your passwords with any other devices?
If so, are you seeing the same behavior on your other devices?
Additionally, are you experiencing this behavior with any other websites?
Let us know, and we'll keep moving forward based on those details.