I think that the “circle to search” feature is a bit overrated and mostly just marketing.
I have integrated the google assistant into the “press and hold power button” feature and after using it I choose “seach on screen”.
For me it brings the same results with maybe one more second of effort. This feature can even recognise text and symbols so that you can copy them. Give it a try :- ) For me there is no need so implement circle to search.