Worked for me. Installed it from a modified deb, apt keeps wanting to update it from the one in the ppa but it won't as long as the conflict is still there.

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Yes, libraw20 breaks libraw19 because the deb control has libraw19 set conflicts and replaces. Replaces shouldn't be set because it doesn't overwrite anything. I'm not sure if there is actually a conflict but there doesn't seem to be.

You can get it to install if you download the deb:
apt-get download libraw20

Unpack it:
ar x libraw20_0.20.0~202008211452~ubuntu20.04.1_amd64.deb

Unpack control:
tar -xf control.tar.xz

Edit control:
delete Conflicts: libraw19
delete Replaces: libraw19

Repack control
tar --ignore-failed-read -cvzf control.tar.gz md5sums control

Repack the deb
ar rcs libraw20_fixed.deb debian-binary control.tar.gz data.tar.xz

Install
sudo dpkg -i libraw20_fixed.deb

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