"Preferred network type" menu only shows 3G

Hi there. Got a new BV9800 (not Pro, but your site won't let me select that). I'm stuck with 3G despite the fact that my previous phone (a Moto G6) was happily connecting to 4G on O2/Giffgaff using Band 20. The BV9800 doesn't show me any preferred network type option except 3G; other choices aren't greyed out, they're simply absent. I'm in UK;  phone was sourced from UK Blackview outlet and came with UK charger.