The bottom line is that if you become a doctor, you will probably no longer keep shabbos. Whether that is muttar or not, you can ask your rabbi. But it’s not shabbos.
And no, it is way different from for example being in hatzala where you regularly do melacha on shabbos for specific pikuach nefesh situations. Doctors treat shabbos like any other day.
As the gemara says, they go to gehenom.