That is what the underside of the originally pictured plant looks like. It smells fine and the roots look generally ok to me so I’m not sure that’s the issue here.
I have grown some plants before and currently have a calendula and some basil plants that are doing just fine in the same tent.
https://www.mdpi.com/1420-3049/26/14/4113 In this paper it seems to suggest that you would be fine decarbing up to 135°C (or 275°F) but at that temp you would only want to decarb for ~15 minutes (based on figure 8).
Based on figure 7, decarbing at 115°C (or 240°F) for 30 minutes would convert just around half of your THC-A to THC, so 60 minutes would convert around 75%. Most places recommend something around this level because it is easier to not mess up 30-60 minutes than to not mess up not more than 15 minutes, and you don’t need to convert ALL of it in order to get a functional product.
Disclaimer: I have relatively little experience making edibles.