It’s been done.
You can do the complicated way, power bank with USB PD support and a trigger cable that selects the voltage you want. I’m sure I read 12V is now deprecated. The downside with that is you will have another switching PSU right by your radio and antenna. You may be lucky and buy a power bank that is RF quiet. My view is it’s more likely to squag from DC to Daylight so why take the risk.
Just buy a USB power bank that takes 18650 cells. Put 3 cells in the power bank for transport through customs. Remove the 18650s and put them in a 3 cell holder wired for 3S1P to power your radio. No PD issues to deal with. The security people see a USB power pack like the other millions of them they see daily.
See Using 18650 LiIon cells I got the idea off Luc ON7DQ
Works fine with KX2/817/818/705 radios.