The firmware hasn't changed since December 2019 (and you don't need to upload it to the Mega, unless it has been updated). The plugin simply sends the formatted data to the board, and if there is no output, that means the board has not received data to display.
So, you don't need to “check the signals” on your board, you can be sure the outputs are working as long as the Mega received correct data from the plugin (if it is not damaged physically of course).
You need to check your configuration and wiring. Remember what you have changed earlier in your config (before new update)
What was your last version of the plugin before the update? You probably just need to load the cfg file into the configurator and save it again.