WG is not meant to be a stealthy protocol and is easy to detect at the ISP level. It has distinct characteristics that packet inspection tools can use to identify it by examining the traffic and block or flag it.

There are modified versions like AmneziaWG that make it stealthier, or alternative protocols built to evade traffic inspection like xray or sing-box. It’s a bit of an arms race for packet inspection tools to be able to reliably identify these intentionally stealthy protocols, but the advantage is generally strongly in your favor.