Finding installed packages not supported by the Ubuntu team

You can use ubuntu-support-status command

$ ubuntu-support-status --help
Usage: ubuntu-support-status [options]

Options:
  -h, --help          show this help message and exit
  --show-unsupported  Show unsupported packages on this machine
  --show-supported    Show supported packages on this machine
  --show-all          Show all packages with their status
  --list              Show all packages in a list

with corresponding argument --show-unsupported.

Below is example from my 16.04.5 LTS system:

$ ubuntu-support-status --show-unsupported

Support status summary of 'hostname':

You have 94 packages (1.9%) supported until April 2021 (Community - 5y)
You have 2668 packages (54.0%) supported until April 2021 (Canonical - 5y)
You have 647 packages (13.1%) supported until April 2019 (Community - 3y)

You have 79 packages (1.6%) that can not/no-longer be downloaded
You have 1456 packages (29.4%) that are unsupported

No longer downloadable:
acroread acroread-bin:i386 cpp-4.4 cpp-4.5 cpp-4.6 
... 

Unsupported: 
abiword-plugin-grammar adequate aglfn alien android android-tools-adb 
android-tools-fastboot ant ant-optional antiword apt-file
...
y-ppa-manager yad zenmap

(I added the ... to limit number of lines).

sudo apt install synaptic

Open Synaptic Package Manager. Go to "Origin" (bottom left).