On Windows you can find your saved presets folder using the "Run" dialog by pressing Windows+R and then pasting in "%appdata%\\Anthropics\\PortraitPro\\UserPresets"
If you copy these files to the same location on your other Windows PC, they will then be available in PortraitPro the next time it is launched.
On a Mac open the Finder view, then click on Go. Hold down the Option key (ALT on non-Mac keyboards) and click on Library, then navigate to /Application Support/Anthropics/PortraitPro/UserPresets and if you copy these files to the same location on your other Mac, they will then be available in Portrait Pro the next time it is launched.
The preset files can also be copied between Windows and Mac computers.