As mentioned above only PSA, PDT, and Envoy have a flow, Endeavor is only an SSP meaning you reach certain criteria and get the opportunity to interview. Much different than a flow where when your number comes up off to class you go
Back to the OP's original question, I flew with many crew members who took a million different paths to get there.
I'd suggest looking st FAR 61.159 and 61.160 as you'd need ATP mins (61.159) or see if you can qualify for some form of the Restricted ATP (61.160) but there are many intricate requirements, 50 multi (25 in a sim as part of airline training can count) a certain amount of night pic, etc, so read the requirements, find a way that works best for you to hit those time minimums, get the time, apply, go to the airline. So long story short you need a commercial multi-engine land with an instrument rating and meet the requirements of 61.159/61.160
The airline bretheren and sisters on this forum will agree with my next statement. Seniority is everything! So if that's your goal my personal recommendation is get at it! Good luck!
I enjoyed my time in the regionals and now there's a lot more money on the table at them than back when I was in and started