@DerMartin did you manage to get lensfun installed and updated? I am fighting with lensfun-update-data, it always crashes. Tried to deinstall, reinstall, compile … everything. Liblensfun is installed and seems to work but interestingly only with a very old/limited set of lenses and I have no chance to update lensfun data.
About dt on Ubuntu 20.04:
manual build from git worked for me with 3.01
tried to get 3.02 with snap installation - but even today its only 3.01
connected the ubuntuhandbook ppa to get 3.02 (successfully)
fighting with lensfun in all variations 