Photo Retouch Help

The Neural Filter you need is "Photo Restoration." It has, among other things, a "Halftone artifacts reductions" slider. Ignore the other Neural Filters, because they will not take you where you need to go.

Before and after running that filter on a scanned halftone printer image.

The thing is since it's a high res scan of original art, it's highly pixelated.

By @Rafael26281653wpvv

That doesn’t make sense…by definition, a high resolution scan of original art should not be pixelated.

Do you really mean that it’s a scan not of the actual original artwork, but of artwork reproduced by a printing press (a record album cover)? If so, then it sounds like what you are seeing is not “pixelation” (square pixels) but the four overlaid halftone screen dot patterns for the CMYK inks laid down by a printing press, as shown in the picture below. Is this what it really is?

If so, then the solution you need is to “de-screen” those halftone screens. There is no “de-screen” filter in Photoshop (Edit: AlanGilbertson’s post below does list an option in Photoshop), but there are some manual techniques published around the web and on YouTube. Some scanner software has a de-screen option, but of course you have to apply that at scan time, and it’s not perfect.

Because a halftone reproduction doesn’t have the full information of the original artwork, the results of de-screening a reproduction will not be as good as scanning the actual original (not reproduced) artwork.