do i need to disconnect from ethernet to connect with wifi

No, you do not need to..

However, you can go to "System Preferences" --> "Network" to choose which connection method as your priority (Set Service Order). My iMac desktop connects to ethernet (main) and WiFi (for airdrop purpose) at the same time. Although, I usually disable the WiFi unless I need it.

ps: the below picture was under Big Sur on my Mac Mini (WiFi connection only).

I would add the following comment. Why would you prefer Wi-Fi over a hard wired connection? Wi-Fi is often slower and not as reliable.

That’s not true, lots of “it depends”. You can’t generalize.