Checked the supply on this site and they are shipping within ten business days. Just spoke with my favorite local Titleist account, they are on allocation and will be thru December. She is a LPGA pro and does the buying and said she is not aware of the reason for the shortage. Might have some luck getting them at pro shops or locally owned shops.

Haven't heard this and have seen stocks at places I visit

During COVID there were shortages of the ionomers for the mantle layer of the Pro-C’s as well as the covers on 2 piece balls. This slowed production along with factory shutdowns.
Titleist uses a proprietary urethane formulation. Prior to the 2023 release, plant #3 was running full speed with no mention of any supply issues slowing production.
I suppose in the good news/bad news area either Titleist is not impacted like other vendors or if anything goes wrong with a sole supplier, there isn’t another source to tap. On the demand side they were still working to saturate the pipeline. Maybe demand is up yet again this year.

Your friend didn’t by chance recommend their tour urethane ball as a substitute? The price jumped 60% in a year. They may have a larger inventory this year. ;-)