Does he? In that case, you have Paul flat-out contradicting himself! So either Paul is very confused … or you are very confused and your doctrine doesn’t add up. I suspect the latter is true.
What you don’t seem to understand is that “the law” Paul refers to in Gal 5:4 is not all 613 laws of Moses, but only the ceremonial and ritual laws that Jesus rendered obsolete, such as circumcision (which Paul specificaly refers to in that same passage).
In Gal 5:4, Paul is not referring to the MORAL laws of Moses - the MORAL laws of Moses are ETERNAL and STILL APPLY TO CHRISTIANS. This explains why Paul warns Christians later in Gal 5 that their sins (“works of the flesh”, v.19-21) can result in them not inheriting the kingdom of God (v.21).
It also explains why Paul refers to the obligation of Christians to fulfill “the law” in Romans 13:8-10 - he is referring to fulfilling the moral laws of Moses.
In Romans 6, Paul explains the need for believers to say “No” to sin and “Yes” to deeds of “righteousness” in order to gain the “sanctification” that leads to eternal life. By “righteousness” he is referring to keeping the moral laws of Moses.
In Romans 3:31, Paul says “we uphold the law” - once again he is referring the need to keep the moral laws of Moses.