Thnks @dan.woda for you response.
I know the proposal of each APP (Regular web application, Single page web application (SPA), Native application)… I understant the importance of “Client Secret” is for backend use only…
I tested each APP… for example: I tested (without Client Secret) “Regular web application” and “Native application” in React (SPA)… And I tested a “Single page web application (SPA)” and “Native application” with nodeJS and php (with Client Secret)…
In the two tests, the Auth0 “Applications” worked the same way, I did not see any difference between the three Auth0 “Applications”, even the settings of these three Auth0 “Applications” were the same.
When I tried to use Auth0 application “Machine to Machine (M2M)” with ReactJS (front) and NodeJS-PHP (backend) it didn’t work (try to verify token). (I had expected functionality, it only worked for machine-to-machine communication.)
I have not yet tested the operation of the three previous Apps (Regular Web Application, Single Page Web Application (SPA), Native Application) trying to make a Machine to Machine communication, I hope that with these three applications it does not work.