For Ubuntu 20.02 amd64 on PC, try same instructions as for Ubuntu Server 20.02 arm64 on Pi4, taking care of these 2 points:
(1) In following dpkg commands replace package names with arm64 by name of packages you have actually built
$ sudo dpkg -i librtlsdr0_0.6_arm64.deb
$ sudo dpkg -i librtlsdr-dev_0.6_arm64.deb
$ sudo dpkg -i dump1090-fa_3.8.1_arm64.deb
$ sudo dpkg -i tcl-tls_1.7.16-1+fa1_arm64.deb
$ sudo dpkg -i piaware_3.8.1~ubuntu1804+1_arm64.deb
(2) Dont forget to mask as follows
## Issue following command to prevent Ubuntu from replacing above
## installed packages by packages from repository during any unattended upgrade.
$ sudo apt-mark hold librtlsdr0 librtlsdr-dev
## Issue following command to prevent Ubuntu from replacing above
## installed packages by packages from repository during any unattended upgrade.
$ sudo apt-mark hold tcl-tls