AIFMD is a European directive, and as the UK is no longer part of the European Union, the original directive does not apply.
However, the UK has maintained its provisions that were adopted into National Law under AIFMD prior to Brexit. Essentially, there are two regimes that are quite similar, but UK managers are not EU AIFMs, and they cannot get a passport using a UK manager. They will have to make their registrations in various jurisdictions, and they cannot use their UK entity under the AIFMD passports for marketing.