R2 Trigger not responding at all

Hey guys! So I've had my DS4 for about 6 years now. I didn't use it for a while (about 2 years), and when I plugged it in the other day (I use it on PC, my PS4 doesn't work) the R2 trigger wasn't responding at all. It's not a flicker or a "I have to press real hard" thing: it's completely dead.

I opened the controller to check for any obvious signs (broken plastic, something missing, something burnt), but honestly couldn't find anything. I even took it off and tried pressing the sensor myself and nothing (I did the same with the L2 trigger to compare, and it responded perfectly). I used DS4Windows to test the buttons' response.

So that's the extent of my "knowledge", I don't know electronics enough to really know what's wrong other than what I did. Is there anything else I should be checking? Like something in the motherboard, or maybe a cable/flex I don't know about? I didn't take the battery off to expose the motherboard because I wouldn't know what to look for before asking.

I don't have the money to buy a new one right now (plus the rest of the controller works perfectly), and would like to avoid sending it to a "technician" to be charged a lot for something I could fix myself.

Thanks in advance for reading and any help you can provide!