You can use the same license on up to 5 different computers both macOS and Windows.
The Guitar Pro 7.6 license agreement states among other:
"The License acquired hereunder may be used to activate the software as many times as desired, within the limit of up to 5 computers at the same time. Beyond these 5 computers, the User shall first uninstall the software before installing it on a new computer. In any event, the use of the License on multiple computers is limited to the different computers of the User, and their family environment in the case of private use."