My 9 month Old Acer Nitro 5 (AN515-52) is working perfectly till 10 days ago and suddenly It's start overheating for no reasons with very low cpu usage like 10-20%. even running youtube would cause cpu temp to rise 96 degree with 10% cpu usage and it stay at 90 degree and even small games(Mobile games on emulator) causing cpu temp to rise and stay at 95 degrees with so much lag at only 35% cpu usage because of overheating. at this point I cant even think of playing medium graphic games.
Just 10 days before everything runs without overheating Like I used to play youtube videos of 4K 60fps and still temp stable at 60s n 70s and play same mobile game on emulator at it's max 60fps on high settings without lag with cpu temp at 70s.
and suddenly what happened I don't know and now any app or process cause cpu temp to jump 90 degree, Like play 720p movie in vlc player and cpu temp is 90-93 degree or open youtube 10 min video at 720p cause cpu temp to 90s degree. running any game is not possible without so much lag. and this overheating issue started 10 days ago.
I always use my laptop on AC power and when gaming always use fan speed at max 6122 rpm with coolboost on. 

So tried these solution already:
1. first I change thermal paste using Arctic MX-4 but no help temp still high, so I again change paste using Coolermaster MasterGel Pro but still temp in 90s degrees.
2. I already using colling pad of Coolermaster all time and bought new cooling pad with 4 fan of turbo speed and it's barely lower the temp 2 degree.
3. Tried to off Turboboost and temps got lower to 70s but every process running slow and my 60fps game drops to 40fps with heavy lag because my cpu stuck at base speed of 2.20 GHz so no help.
4. Tried some graphics setting changes and other changes suggested by forum moderator but no changes on temps.
5. And finally tried undervolting the cpu using Throttlestop with given profile (Throttlestop profile already tested on i5 8300H) and while gaming Emulator game(PUBG Mobile) temp stays at 70s and 80s degree but because of undervolting cpu speed set max at 3.39 GHz my game FPS drops almost 15-20 and stuck at 45fps and also lags frequently. A 60fps game running at 45fps with lag is like I playing on i3 processor with Intel graphics. Using Throttlestop temps got low but this much sacrifice of fps with lag is not worth it.

I'm using Throttlestop from last 7 days till yesterday I haven't start Throttlestop undervolting and just randomly closing apps/processes and after 10 seconds temps got stable at 60s even a youtube fullhd video is playing So test this more I started 4k 60fps video and still temps at 65-75 and finally I run same emulator games and games running smoothly at 60fps with temps 70-80 with no lag at all. 
at that time I didn't know what have I closed and this happens so I haven't shutdown/restart my laptop for like 14 hours straight just enjoyed those hours with no overheat.
But guess what today when I start and hoping no heating but no It again start overheating for no reasons same 90-97 degree for everything. And now I don't even remember which app/processes I closed to solve the issue so I tried again closing randoms processes again but no help.
please help me.