So you use a wired network connection for the initial connection and setup of the R Pi.
Then when all is finished you disable to Wi-Fi interface of the R Pi.
Then you are no longer able to connect to the R Pi with the browser or app?
This seems odd, are you perhaps inadvertently using a Wi-Fi connection during the initial connection and setup?
What if you disable to wireless interface on the computer you’re using for that initial connection and setup.
Once you’re connected and working on the new install, run a ping to volumio or volumio.local, see what the IP address is, note it.
This will be the IP address assigned to the wired Ethernet interface of the R Pi.
Then if you have weird behaviour after disabling the Wi-Fi interface of the R Pi, you can try the IP address you noted instead of using the dns name.
IE. Enter the IP address into the browser address bar in place of volumio or volumio.local