Hi @yogi27770
The WiFi and Bluetooth and hotspot all use the same antenna so try using the WiFi as close as possible to the network router i.e. <10cm and check if the number of WiFi signal level bars increase.
If they do it may be a loose antenna connection that is the problem.
Here's an image taken at 3:19 minutes into this [https://www.youtube.com/watch?v=hqsuSiZrbgc|video] which shows where the two ends of the antenna are connected to.
[image|3145552]
(click on image)
if the antenna is OK then the [https://phonelumi.com/samsung-galaxy-a21s-sm-a217f-schematics/|schematics] will be needed to help to find the problem on the systemboard.