Looking at the build log of pyfai, I can find this https://launchpadlibrarian.net/501584970/buildlog_ubuntu-groovy-armhf.pyfai_0.19.0+dfsg1-3build1_BUILDING.txt.gz
Selecting previously unselected package python3-silx. Preparing to unpack .../238-python3-silx_0.13.1+dfsg-1_armhf.deb ... Unpacking python3-silx (0.13.1+dfsg-1) ... Selecting previously unselected package python3-silx-dbg. Preparing to unpack .../239-python3-silx-dbg_0.13.1+dfsg-1_armhf.deb ... Unpacking python3-silx-dbg (0.13.1+dfsg-1) ... so it seems that this was rebuild with the wrong version on silx. not the one rebuilt with python3.9 support. I guess this by looking at other packages which containes Selecting previously unselected package python3-scipy-dbg:armhf. Preparing to unpack .../237-python3-scipy-dbg_1.5.2-2build1_armhf.deb ... Unpacking python3-scipy-dbg:armhf (1.5.2-2build1) ... the build1 version :)
