They also updated the game's entire "engine" it runs on, which in addition to all the stuff like graphics and user interface, it also handles physics related things.
Since your Celeron is from 2008, it is only a Single Core CPU (lacking even basic HyperThreading). So my guess is that the issue is actually your CPU being TOO overloaded.
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You might have better luck trying to turn settings down instead of up. :(
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But to directly answer your question:

Is it my specs or the game????????

I think it's a bit of both. Your computer was never meant to play games, even when brand new. Only as something for typing documents or light internet usage.

@SimpleUser1938 put simply, I don't think you meet the system requirements.
Ideally you would be running at least a Core 2 Duo L7100 or amd a4-9120 or better, with integrated graphics. Most of the APUs built after about 2012 I think use the computer's RAM for their vram.

Personally, I would recommend getting a pc with at least a Ryzen 3 2200g or i3 7100, and about 8gb ram for a better experience. If you can get your hands on a pc with a Ryzen 5 5600g or similar you will have far better performance I think.
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Obviously it's impossible to rule out a bugged SimplePlanes, so try first disabling mods, and if that doesn't work - if you got it through steam I would recommend backing up planes and mods and reinstalling the game. If THAT doesn't work, the above hardware statement is true.

after the update it got buggy

@ZWLenning i bought simpleplanes for pc like a year ago

its a intel celeron 585 with integrated gm45 graphics

do you know your CPU and GPU? its possible that you don't meet the minimum requirements - specifically GPU and RAM