I use the Create Modern SharePoint Site action and the external sharing option is always disabled by default. The Tenant does allow external sharing. Is there a way to modify this option through Power Automate and Plumsail actions?
The default sharing settings are defined by Microsoft depending on the site type and Plumsail Actions cannot change it. Please check this article.
And these settings are not default but maximum allowed permissions for external sharing. In other words, you can't set the external sharing more permissive for a site than it is set here:
Bug again, it is not the default values. To allow external sharing by default, create a team site with a group.