I would like to know if it is possible, in case I regret the site I made, to install the theme I bought on a new site from scratch
All of the themes on the Envato market are under the same license, details: https://themeforest.net/licenses/standard.
You can use one license per end product to use any pre-built website you desire or mix them, but you cannot use the theme license on two domains.
The only exceptions are for subdomains or subfolders. You can register unlimited subdomains with one license key, as long as the main domain is registered under the same key.
This also applies to subfolders on localhost installations.
So yes, if the previous website is not in use anymore, and it was deleted, you can use your license key on the new one.
thanks for your help