Is there a 1/2 Female copper to 3/4 Pex barb adapter?
Yes, it's called a &quot;1/2 in. Brass Female Sweat Copper Adapter x 3/4 in. Pex Barb Pipe Fitting&quot;
Home Depot | Amazon

Sidenote: it took me quite some time to become efficient for searching these kinds of parts.

Per your comment this part is unavailable to you so you can do this:

Get a 1/2&quot; female sweat to 1/2&quot; barbed adapter

If available then do a 1/2&quot; push-to-connect coupling instead since it will help to avoid soldering


Attach a short (6-12 inches) piece of 1/2&quot; pex
Get a 3/4&quot; to 1/2&quot; barbed transition

Not sure about your pipe layout but a 3/4&quot; to 1/2&quot; barbed elbow could be a better choice
3/4&quot; x 3/4&quot; x 1/2&quot; reducing tee could also be used depending on where this transition is