[2021-08-17] Accepted kdenlive 21.04.3-2 (source) into unstable (Patrick Matthäi)
Currently version 21.08 is installed without any problems
# LANG=C apt policy kdenlive kdenlive-datakdenlive: Installed: 21.04.3-1~np1 Candidate: 21.04.3-2 Version table: 21.04.3-2 500 500 https://deb.debian.org/debian unstable/main amd64 Packages 500 https://incoming.debian.org/debian-buildd buildd-unstable/main amd64 Packageskdenlive-data: Installed: 21.04.3-1~np1 Candidate: 21.04.3-2 Version table: 21.04.3-2 500 500 https://deb.debian.org/debian unstable/main amd64 Packages 500 https://incoming.debian.org/debian-buildd buildd-unstable/main amd64 Packages
deb https://www.deb-multimedia.org sid main non-free