Adobe no longer supports Acrobat Reader for Linux. The latest native Linux version is 9.5.5 dated from 26/04/2013, as you correctly stated in your question. Maybe, the only chance to use a newer version is installaing the Windows version through Wine, but

Install Foxit PDF Reader on Ubuntu 20.04. After extraction, you should have an installer in place; ls -alh-rwxr-xr-x 1 gentoo gentoo 85M Sep 11 2018 'FoxitReader.enu.setup.2.4.4.0911(r057d814).x64.run'-rw-rw-r-- 1 gentoo gentoo 71M Sep 14 2018 Fox

Run system update command, to make sure all the packages are in their latest state: sudo apt update Install Dependencies. Being an older version it needs some i386 packages that are not going to install by default on Ubuntu 20.04 or 18.04 while installing