Is this melted spot inside my freezer normal or a fire risk?

That long raised bump is the cover over the evaporator coil and the defrost heater. Nothing fancy lives in the bump itself, it's mostly a channel that hides the coil, the heater underneath it, and the little drain path for defrost water. The orange fibrous stuff is just fiberglass insulation from behind the liner, so touching it won't hurt anything, but it means the liner has a hole or melt-through at that spot and cold air or moisture can get back there now, wich causes frost problems of its own.

As for what cooked the plastic, on these models the usual suspects are the defrost heater running way too hot or stuck on, or heat damage from a previous repair. Techs sometimes braze or use a heat gun back there and don't shield the liner. Since yours hasn't been opened up before by the sound of it, factory damage or a heater running hot are the two real possibilities. The fact that you also have recurring warm-freezer episodes makes me lean toward the heater or the defrost cycle misbehaving, because a freezer that slowly thaws while the fridge side stays fine ussually means the coil is frosting solid and airflow dies, not that the sealed system is shot.

Easy check: pull that panel again and look at the coil. If it's a solid block of ice, your defrost is failing, and that lines up with the every-few-months pattern perfectly. Frost in one corner or a light dusting is normal.

One caution, unplug the fridge before you go poking around back there, the heater wires and the fan are live with the door switch bypassed once the panel is off.

If it turns out to be the heater or a thermostat, that's a cheap-ish parts fix you can do yourself. If the liner damage is bad, you can seal the melt spot with foil tape made for appliances so insulation stays dry. I wouldn't shop for a new fridge til you've confirmed what's actually failing.

Had almost the same thing on a Whirlpool I fixed for a buddy last year, same liner melt right over the heater channel. I checked the heater with a meter and it read about 15 ohms, which was in range, but the defrost thermostat was sticking closed and cooking everything during the cycle. Swapped the t-stat for under 30 bucks and it's been fine since. Worth testing both parts before you blame the heater itself, they're cheap and you can ohm them out in ten minutes with the panel off.

Ran into the same kind of melt on my old fridge a few years back. Mine turned out to be a clogged drain line, the defrost water had nowhere to go so it pooled right against the liner and eventually ate thru it near the heater channel. Cleared the drain with some hot water down the tube and taped over the spot with foil HVAC tape. Two years later it's still running fine. So before you assume the heater is bad, blow some air through that little drain tube under the coil and see if it's plugged. Cheap to check and it explains the every-few-months pattern too.