Roth IRA: 100% VT? Or 35% VXUS and 65% VTI?

Basically the title. I’m 24, just now opening a Roth IRA. I’ve done some research, but all this is hard to wrap my head around.

The primary recommendation I’ve seen is either 100% VT, or 35% VXUS and 65% VTI. Is one more preferable to the other?

Also, does it matter if I use Fidelity or Vanguard?

Thank you in advance 🤍