app or widget or other solution for turning just cellular radio off/on I recently acquired an umidigi one with android 8.1 oreo naked/stock image in place and voice over wifi as well as voice over lte support.  

When device is in location with wifi connection, which is most of the time, i want quick way to disable cellular radio to force a voice [ and text ] over wifi connection to be established and to conserve battery power that would be otherwise expended on the cellular radio at these times. 

Currently i am accomplishing this by selecting airplane mode and then re-enabling wifi to leave me with just cellular radio turned off thus forcing the voice [ and text ] over wifi connection to be setup.  Its a cumbersome two step process and a three step process if i also want bluetooth radio enabled at these times.  

Its unfortunate that the drop down menu "mobile option" doesn't turn off cellular radio voice as well as data services instead of just mobile data services.  

Also would be nice to have a configuration option that would tell phone to establish voice [ and text ] over wifi if wifi connection is present and only resort to voice over lte or 3g/2g gsm connection in the event that wifi is not present as opposed to now where it does the reverse and only uses voice [ and text ] over wifi when cellular options are not available.
Well you can always use Tasker.

More information on how to use tasker at: https://tasker.joaoapps.com/userguide/en/index.html