1)Shadows looks really bad,how can i increase the overall quality of scene so that shadow gets better and flickering is removed?
try tweaking shadows params as shown here
https://www.soft8soft.com/docs/manual/en/blender/Shadows.html
Reflection doesn’t look right after i have exported as Gltf as they look in blender. I can only see HDRI reflection on the reflective sphere and not the geometry reflection.
for reflection you can use the puzzle screen space reflection/refraction
https://www.soft8soft.com/docs/manual/en/puzzles/Postprocessing.html#ssr
3)Is there any tutorial on how i can setup walk mode for the scene?
not yet but the setup is simple: you can switch the camera to first person mode and assign a collision material.
Is it possible to create different camera angle buttons? so that user can user can navigate to different view after clicking some button?
sure, you can control camera movement with camera puzzles
Can it handle bigger scene like in the below example if we have 10 more of the same geometry?
yes!
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