You do not specify the pathway leading to the result that (old 1.2.0) Avogadro did not install when compiled from source or using a .deb. (I think the distribution of portable AppImages for Linux is a recent addition after dropping the development on Avogadro 1.2.0).
The Grimme group (university of Bonn, Germany) offers a container to work with old Avogadro (post by Geoffrey in the forum, and the GitHub repository). Do your attempts already include testing this option?
If this doesn’t work well enough, there still is the option to retain/install a spare instance of e.g., Xubuntu 18.04LTS (Bionic Beaver) with old .deb packaged Avogadro side by side to the LTS of 20.04 (Focal Fossa)/contemporary 22.04 (Jammy Jellyfish) on the same computer. A multi-boot installation can be set up to either a) let both Linuxes access the same home partition, or b) that there is a small logical partition just to shuttle the relevant data back and forth.