I own some cameras- and a Therm-App of mine once looked at a reflection of the Sun apparently at a glimpse in my car, because when i next looked at it it had a bright streak on it(to this day I don't know if it was actually the sun that caused this, as thermal doesnt go through glass....)- it took far longer than you'd EVER guess for that to 'fully'dissipate - months(left a bright streak which became a clear streak which then completely dissapeared)
That was a odd case.
But the therm-apps are funny- I once looked at a toaster with it, and then when i looked away, i saw minor streaking from it- and i know for sure it was the toaster, this time- that went away very fast.
So, it's hard to tell- but intense IR sources will overcharge the camera a little bit, and NUCs don't fully get rid of it- time does though.
Meanwhile my Pathfindir II , is built for sun exposure, (plus it's one of FLIR's Vanadium oxide sensors)- and if you drive into the sun, (I turn it off when possible to avoid this), it'll be fine- but if you keep going into the sun, when you finally turn away, it'll have bright spots/streaks also(not like the therm-app did), although a few NUC's will clear it.
Fun fact: when shooting videos, i've looked at the low hanging sun with my therm-app- the Sun did not affect it at all then , so I suspect if it's high noon, you're in trouble- but if its sunrise or sunset, it's the same as with our eyes- it's safe immediately when the sun is coming up or down