Optical zoom, using the lens to zoom in/out to make the image smaller or larger, should not impact image quality in any way on a quality projector.

Most quality projectors have some optical zoom built in. Epson, on their better models, like the 4010 or 5050, have over 2x optical zoom. This means you can turn a 90 inch diagonal into a 180 inch diagonal from the same distance. Typically, somewhere in the middle of the zoom range is used to give the installation a lot of flexibility.

Do NOT use digital zoom.

Digital zoom degrades the image.
Keystone correction degrades the image.

Any digital image correction features degrade image quality and should be avoided. Instead, place the projector accurately, where it needs to be placed, then use optical zoom and optical lens shift - if available - to adjust the image placement.

If no optical zoom or lens shift is available, you MUST place the projector precisely for best image quality results.

Quote (doctort on Oct 18, 2022 1:38 AM): digital zoom degrades the image quality even if one will make the image larger a little bit through digital zoom?

You can't make an image 'larger' with digital zoom. Only smaller.
Let's say you have a projector with resolution of 1920x1080. It won't be possible for that projector to have MORE resolution than 1920x1080, and to get the best image, you don't want to use any digital correction, or you will have LESS than 1920x1080 resolution.

The lens itself will determine how far from the screen the lens must be (throw distance) to get a specific size.

If you own a smart phone, you already know this is the case. To get a photo of your door, you have to be a certain distance away. If you are any closer, you absolutely can't capture the entire door in your photo.... So you back away from the door. If you back up too much, the floor and ceiling will be in the photo. If you pinch to zoom, you are digitally zooming in, and this will lower the image quality of your photo.

Quote (doctort on Oct 18, 2022 1:38 AM): ...what is optical zoom?

Optical zoom, is what is common on actual cameras (not phones). It uses several lens elements on the front of the projector which when moved closer/further from each other, allows you to make an image larger or smaller.

Quote (doctort on Oct 18, 2022 1:38 AM): the quality of the image will not effected in a bad way no matter there is how much distance between the projector and the screen?

If you want, for example, a 120" diagonal image. And your projector has a lens which optically allows you to place the projector from 10 feet to 15 feet lens to screen (throw distance), then there should be no change in the image quality.

Quote (doctort on Oct 18, 2022 1:38 AM): even if one will place the projector at the huge distance from the screen to make the image larger then it will not effect the image quality in the bad way?

That's a different question. A 240" image is 4 times the size of a 120" image. So, the pixels will be four times as large. It will be a degraded image, and only 1/4th the brightness. Image SIZE impacts image quality, but distance does not if the screen size stays the same.