An unstable wifi connection in a new iMac

Hi,

I bought a new iMac in 2 months ago. From the beginning, a wifi connection is very unstable. Every 5-15 min, the computer is looking for wifi connection. While this, I can't use internet and am kicked out from Zoom meeting. This is frustrating as the computer is new. Wifi itself in my office is stable as other MacBook Pro and old iMac provide very stable wifi connection. First, I contacted Apple support, but they could not resolve this issue and recommended me to go to an Apple store. I went to Menlo Park Apple store in NJ, which tested my iMac and said that everything is fine. They erased HD and reinstalled. But the unstable wifi situation continues. I called to Apple store again and went the Apple store Menlo Park again, but the manager said that they can't do anything for this issue as they tested my iMac Before. Now I don't know how to resolve this issue by myself. The store said that buying a new computer is one way to resolve this issue.....why I have to buy one more new iMac? Could anyone in this community helps me resolve this problem? Thank you for your help.