3rd party cookies & Google OAUTH

I started working on server side for my current porject and one of the biggest issues that i facing is with Google O-Auth. Since i am not experienced with the server i decided to use firebase throughout my project.

3rd party cookies are need to be enabled for Google OAuth. I am trying to find my way around it(means: even if the 3rd party cookies are disabled a user can login through google).

First Qestion: Is it even possible?.. i guess it is because i have tried few popular websites like bitbukcet where even if you switch off 3rd party cookies, the O auth works perfectly.

If yes then Second Question: How do i implement it? i was reading some Google Developer docs and found this "another workaround is to implement server-side OAuth 2.0 flows". I really do not understand this.

What i have tried: I have tried two things, first the typical and easier way of going with firebase auth and google login with popup. Second, Login through GAPI AUTH.

I am looking forward to any answer.