2023 MacBook Pro won't mount Dover clip art CDs.

How old are these CDs?

Apple removed all support for the Macintosh HFS (no "+") filesystem in Catalina. If the CDs are so old that they are formatted with HFS, a modern Mac will not be able to read them. Reportedly, even CDs formatted as hybrid CDs – with both HFS and a PC-readable filesystem – will be rejected. Big Sur and later see the HFS filesystem and choke, even if the PC filesystem is also present, and even f they would have been happy to read it (if it was the only one).

If these are Hybrid discs, you may have more luck reading them on a Windows PC than on a modern Mac.

If these are HFS-only discs, you might still be able to read them on a Windows PC with the help of a utility such as MacDrive. (It would depend on whether MacDrive still has HFS (no "+") support.

<< Disc Utility can see the disk when I select, "show all discs", but it won't mount. >>

Please post a screenshot of the Disk Utility screen with that device selected.

Another issue that you may encounter is the removal of built-in support for PostScript. (That is, if you can read the CDs, and then discover that some of the clip art is in PostScript or Encapsulated PostScript form.)

PostScript is the page description language that helped to launch the desktop publishing revolution. But it is also a full-fledged programming language in which someone could potentially write malware to try to affect a printer, or a program displaying a PostScript file.

View .ps and .eps files on Mac - Apple Support

AppleInsider – Apple drops PostScript support in Preview for macOS Ventura

While you may still be able to use third-party programs to handle such files, the removal of built-in support has not gone over well with people who still have a lot of Encapsulated PostScript (.eps) clip art. (And as a practical matter, not a theoretical one, PostScript does not seem to have been an attack vector for a lot of attacks.)