Weird wall shading

[deft vale]

How can i fix it

[stone jolt]

fix what?

if you mean this, then it looks like light leaking

[rain crescent]

99.99% sure it's this.
It can be fixed by having an "outer" geometry to fake thick wall and block external lighting.

[deft vale]

why is this happening

i modelled it correctly

is it a unity issue

should i switch to unreal (but my pc sucks)

also can i make it look like this in unity (its a render in blender cycles)

[desert badger]

It's a rasterized shadow rendering issue
Blender's Eevee has the same issue for the same reasons, and I'd guess Unreal likely has it as well
Like Remy says, block the light outside of the room with additional geometry

[desert badger]

Cycles is a path tracing renderer, so no realtime game engine can truly replicate its results (except HDRP's path tracing, but arguably that isn't "realtime")
Your first option is baked lighting, as it is performant and also uses path tracing
Though since it's precomputed, it can't handle specular reflections so those would have to be approximated with reflection probes
Your second option is HDRP's realtime ray traced reflections and RTGI, which can get very close to the target, but with neither very high performance or quality

[stone jolt]

it is common in any rasterized rendering

unreal will have it too

except for VSM, but you said your pc sucks, so it can't handle it

[deft vale]

What is a vsm?