Brexit visa - going from temporary to permanent

Hoping a Brit somewhere has been through this already and will take pity on me

I’ve been in Germany, Frankfurt area, since 2019 (now over 5 years of continued residence) and was issued with the standard Artikel 50 Aufenthaltstitel Brexit visa.

Now that I’ve been here over 5 years I’d like to change to a permanent visa type mainly because it gives more flexibility to leave the country.

What I am unsure of is what I should be changing into. My understanding is that is there is some sort of Daueraufenthalts­dokument-GB option which is the permanent version. But is this basically just the standard permanent resident permit , or some special Brexit thing. On the Frankfurt Ausländerbehörde site what visa type should I be applying for ?

I actually sent this question to them via email and they just replied with a link for an extension to Brexit visa form - not convinced that’s right?

Thanks for any guidance 🙏