It is possible to force "4G only" without root. First download "Setting Database Editor" from playstore. Open it and look for "hw_networkmode_preferences". I use this value "9,3,2,1,11" on my phone. Save it and restart your phone. If you still don't get "4G only" option then you need to open the "Setting Database Editor" again and look for "hw_add_4g_only". Mine was set to "250". You need to change it according to your country mobile code. Look for your mobile country code here: <1. o prevent spam on the XDA forums, ALL new users prevented from posting outside links in their messages. After approximately 10 posts, you will be able to post outside links. Thank you for understanding!>. In my case I change the value to "250;502" since 502 is my country code. Save it and restart your phone.
Tested on rebranded P10 Plus 256GB.