hi, im a karaite jew and would like to come back to mainstream judaism, my dad is jewish and my mum is atheist. My parents divorced and i was raised by my dad as a jew. Can i peform a giyur lechumra to convert to rabbinic judaism?

Shalom, Thank you for your amazing question. I say "amazing" because it is such an incredible thing for you, the descendant of the people of Israel, to be finding your way back to your spiritual home after all these generations. Welcome Home! There is quite a discussion as to the status today of Karaite Jews, and the extent to which they need to convert to return to Orthodox Judaism (if at all). (See Shulchan Aruch, Even HaEzer, 4, 37. Also Shut Yabia Omer of Rav Ovadyah Yosef zt"l, Even HaEzer volume 2, 21 and volume 8, 11 and 12). However, all this is only applicable if your mother was born as a Karaite. If she was not born as a Jew or a Kariate (that is if her mother wasn't Jewish or Karaite) then your status is similar to that of other non-Jews who wish to convert to Judaism, who need a full conversion. My advice to you is to find an Orthodox Rabbi you can discuss this issue with. In any event you will be wanting to find a congregation so you can experience the fullness of Judaism as practiced from within a community. May you be blessed in all your endeavors. Blessings.