I can try give some general advice, as I don’t know the specifics of Pixelfed. Presumably it has an API like Lemmy, as third party apps seem to function, so you should check the documentation for getting the number of likes on a post with the API, and write a script to display it on a monitor as text, as it’s unlikely such a script exists already, although it might. If you’re unsure how to code it, I can try help if you need.

Depends on what you buy. I’d suggest not buying an enshittifiable IoT device but something you can control with a microcontroller like ESP32, such as displays that got decommissioned from train stations. You’ll likely have to write code to generate the driving pulses along with making the Pixelfed API calls. Some companies might be still making ones that can be controlled via RS-232 or RS-485, which would be very easy to write code for.

deleted by creator

I bet this is something IFTTT could do.