Route: Kungsleden (Sweden)
Kungsleden (King of Trails) is a hiking trail in northern Sweden, approximately 440 kilometres (270 mi) long, between Abisko in the north and Hemavan in the south. It passes through, near the southern end, the Vindelfjällen Nature Reserve, one of the largest protected areas in Europe. In the winter Kungsleden is a ski trail with approximately the same route.
We have only tidbits about FKTs on this trail:
www.jolandalinschooten.nl/category/ultralopen/kungsleden-ultralopen/ : Jolanda Linschooten, September 2014, self-supported, a total of 8 days, including 11 hours of waiting for boats.
Daniel Roxvret (https://www.instagram.com/roxvret/) has done Kungsleden 480 km in 6 days 15 hours in addition to some other things.
sondreamdahl.com/2017/10/05/fastest-known-time-on-kungsleden-the-king-of-trails/ : Sondre Amdahl did it in 6d2h51m in 2017. Most was with Elisabet Barnes, who quit before the end due to an ankle injury. It seems like their style was "self supported". His TR is in English.