Hi @rohit33152
Try using the phone as close as possible to the network WiFi router or hotspot i.e. <10cm, and check if there's a good, stable connection.
''If so'' it may be a loose or faulty antenna connection in the phone.
Here's a teardown [https://www.youtube.com/watch?v=nB2Ekq8cjC0|video] that will help.
At 4:07 minutes into the video, you can see one end of the antenna cable as it is being disconnected from the systemboard.
At 9:02 minutes the other end of the antenna is seen being disconnected from the charge port board.
If the antenna is OK, here's an image of the ''WiFi troubleshooting'' flowchart, from the [https://www.mobilerdx.com/2021/07/download-samsung-galaxy-m30s-schematic-diagram-service-manual.html|service manual] that may help.
[image|3052005]
(click on image to enlarge)