add specific size options to crop tool

While I agree totally with @Califdan2 and have never ever found a need to crop to specific pixel dimensions rather than an aspect ratio, I know there is a plugin that can do this. https://johnrellis.com/lightroom/anycrop.htm

Where are you printing?

• At home
• At a store, typically a low end photo shop, or department store like Walmart, or a pharmacy like CVS, Walgreen's
• At a photo share site such as SmugMug
• At a Photo Print service, like Bay Photo, Whitehall, etc

Whoa!  Your characterazion of "aspect ratio" is faulty.  Aspect ratio's have nothing to do with measurements like inches or centimeters.  It's a "ratio", not a "Measurement".  

I hsve no idea why you feel the need to go to photo shop to get your desired croppiong.  I assume you goal is to crop so that a an image could be cropped to allow it to exactly fit on a, say,  15" x 20" piece of paper when printed.   Just  use the 3x4 crop ratio.  But let's say you want 7.5" x 13".  Juct make a crop ratio that is 75 x 130.  Eventual printed inches don't matter when cropping as that is determined when exporting or printing.

If you want the exact number of pixels needed to fill a print of, say 15" x 20" (the the print driver doesn't have to figure it out), once it is cropped to that aspect ratio, in the export dialog you can specify the inches along with a PPI (say 300 for a printer that prints 300 DPI) and LrC will figure out the number of pixels in each direction needed for that paper size and printer.

Here's an article on this topic that I posted to my website earler this month that you may find useful.

https://www.danhartfordphoto.com/blog/2024/6/lr021-image-size-aspect-ratio-resolution-and-files-for-printing