If the US leaves NATO, then the largest army in NATO will be Turkey:

Türkiye: 481,000

Poland: 216,000

France: 205,000

Germany: 186,000

Italy: 171,00

United Kingdom: 138,000

Spain: 117,000

Greece: 111,000

Canada: 77,000

Romania: 67,000

Netherlands: 42,000

Finland: 31,000

Czech Republic: 30,000

Portugal: 28,000

With a number of those European nations becoming more and more muslim, could there end up being an islamic NATO?

Perhaps it will change its name.

Perhaps less islamic nations might withdraw.

Perhaps other islamic nations from the eastern leg of the ancient Roman empire may join.

Never mind, it will all be for peace and the greater good - no need for concern - sorry