I may have an intermediate solution for astroberry users.
I've made Debian installation packages for libraw_0.20.2-1 for arm7 (RPI) as a backport of 'bullseye' release. My astroberry version is Raspbian version 10 which is based on Debian 'buster'.
The packages are attached in a zip file and can be tested.
# We have both libraw version 19 and 20 libraries. Now the dirty part: we can repoint the symlinks :
sudo ln -sf /usr/lib/arm-linux-gnueabihf/libraw.so.20.0.0 /usr/lib/arm-linux-gnueabihf/libraw.so.19
sudo ln -sf /usr/lib/arm-linux-gnueabihf/libraw_r.so.20.0.0 /usr/lib/arm-linux-gnueabihf/libraw_r.so.19
# This way only the libraw version 20 will be used.
That's it. Test away. I cannot test myself as my Canon camera is too old and has a broken USB socket.
In case you want to revert :
sudo ln -sf /usr/lib/arm-linux-gnueabihf/libraw.so.19.0.0 /usr/lib/arm-linux-gnueabihf/libraw.so.19
sudo ln -sf /usr/lib/arm-linux-gnueabihf/libraw_r.so.19.0.0 /usr/lib/arm-linux-gnueabihf/libraw_r.so.19
sudo apt remove libraw-bin libraw20:armhf
sudo apt install libraw-bin # this gets you the 19 version back from the repository