It is not on paper. Couple of ms ( 4ms ) is real, except it is not normal 5G but specific superset / version of 5G.
Your network needs to be End to End running on 5G-A ( 3GPP Rel 18 ) with full SA ( Stand Alone ) using NR ( New Radio ) only. Right now AFAIK only Mobile networks in China has managed to run that. ( Along with turning on VoNR ) Most other network are still behind in deployment and switching.