Severe coverage problems with Iphone 12 where 4 g is week

Hi !

i have severe coverage problems with my iPhone 12 where 4g connectivity is weak but signal still there phone will not change to 3g. With my iPhone x I could force it to stay on 3g and connection very good, disappointed and thinking if I should shift back to an older model. My Huawei phone mate30 pro has excellent coverage in same area and I can choose what connection to prefer.. Please fix this Apple 😩