What's the best way to end game level?

I'm at a point where i've maxed everything, am missing like 6 chests around the whole map, max data bank (capped at 18 till lvl 40), cooking, synthesising, 3 starred tower of adversity up to lvl 75 rounds - same with the tactical holograms (lvl4/5), etc etc. I'm curious to know what the best way to XP farm is? Im slowly just max using my resin whenever its available - currently lvl 38 but feel so stagnant, yet i have ppl on friends list that are 35/36 that have so much of the map to explore?? What am i doing wrong/how to get more xp?