I forgot to mention, because it seems from your post you just want to get something ready to go, but there are more Lego-like options for putting together an AR.
Easiest would be to get an already-built complete lower, and complete upper assembly separate and hook em together. Sometimes "complete uppers" aren't sold with bolt carrier groups (BCGs) though and decent BCGs have been difficult to find in stock lately. Bolts are important so I stress decent.
Moving up the difficulty ladder is assembling the whole thing from parts. Doable if you're handy but takes time to build and some specialized tools (roll pin punches, AR-specific vice blocks and a barrel nut wrench if the handguard doesn't come with one). Then there's the time and effort shopping for all of that.
And if you're really feeling handy and have the tools to do it, you can get an 80% lower and a jig and mill out your own, home-made receiver. Then build the rest with parts.