sudo apt list thunderbird
gives me
Listing… Done
thunderbird/stable,now 1:60.4.0-1~deb9u1 amd64 [installed]
N: There are 2 additional versions. Please use the ‘-a’ switch to see them.
so
sudo apt list thunderbird -a
gives me
Listing… Done
thunderbird/stable,now 1:60.4.0-1~deb9u1 amd64 [installed]
thunderbird/stable 1:60.2.1-2~deb9u1 amd64
thunderbird/green,green 1:52.9.1-1 amd64