what mac bok pro will I need to run the latest versions of photoghop and lightroom?

Memory… maximum memory!

You can check the System Requirements yourself but you may want to focus on »recommended«, not »minimum«.

Otherwise it seems a case where »more is better« largely applies (RAM, disk space etc.).  

https://helpx.adobe.com/photoshop/system-requirements.html

https://helpx.adobe.com/lightroom-classic/system-requirements.html

Technically, any Mac that can meets these two criteria:

• The Mac can run one of the last three versions of macOS (macOS 12, 13, or 14), because Adobe and Apple provide updates and support only for the last three versions. Which move up every year. 
• The Mac meets the published System Requirements for Photoshop and Lightroom or Lightroom Classic. 

This means some Intel Macs can run the latest versions of Photoshop and Lightroom/Lightroom Classic.

Practically, you do want to prefer a recent Apple Silicon Mac (M1/M2/M3). They run the software much faster and better, and will be supported further into the future.

Your post is confusing because your title says MacBook Pro (laptop), but your post text says iMac (desktop). The only iMac Apple sells now is a 24" iMac based on the M3 processor. No other screen sizes or processors are available, and it only comes with the M3 processor and only up to 24GB Unified Memory. But it’s a good computer. It will handle light to medium Photoshop/Lightroom workloads. 

But if your documents are large and workloads are heavy, you can consider a MacBook Pro (laptop) or Mac Studio (desktop without display). These can have a more powerful M3 Pro, Max, or Ultra processor, and can have more than 24GB of Unified Memory.

Any current Apple Silicon computer, although the newer M2/M3 models with added RAM (16 or better yet, 32GB) are better.