Do you accept that if the tracks are all different lengths before you add the silence, they will still be different lengths after adding the silence?
If so the best way is to click in each track, press K on the keyboard to move to the end of that track, then generate 1 second of silence. That silence will be selected, so CTRL + C to copy it.
Then repeat the steps for the next track, but after K, just CTRL + V to paste.
It’s probably easier to automate this about 200 files at a time by downloading TrimExtend.ny . To install TrimExtend, put it into the Plug-Ins folder inside the Audacity installation folder, then restart Audacity.
Then use File > Edit Chains to create a Chain containing TrimExtend followed by an Export command.
Then use File > Apply Chain to apply the chain you created to multiple files.
Note - don’t apply the Chain to all 2000 files at once - that is outside the current capability.
Gale