I see a lot of this kind of devices, where they usually have an ESP8266/ESP8285 or ESP32 chip (with WiFi support, and some ESP32 even use BLe), but they also have (at least) a relay to switch the output and often a sensor to measure power consumption. I've never seen one with an RPi, though with the recent RP2040 that might change, as that chip is targetting the IoT market. But it's not nearly as capable as a full-fledged RPi, more in the ESP/STM region.

The program is in the tray icon constantly running

-Contro (August 13, 2023, 05:02 AM)

Which (exact!) program?

after a time of inactivity ?

-Contro (August 13, 2023, 05:02 AM)

What is your definition of 'inactivity'?

How are you going to save the downloaded-state for each file? As a refresh/reload of the page will re-enable any disabled buttons...

If you want an indication of what's been downloaded already, then present the downloads as links, default browser behavior is to give visited links a different color from new links, similar to:
https://www.donationcoder.com/forum
vs:
https://you.never.visited.this/page