As i understand our installation on a communication site was missing the left navigation bar (and perhaps the top navigation bar). This navigation was not needed with the classic forms which had the buttons to navigate. As we understand this was due to being a Sharepoint communication site in stead of a Team site.
We are currently using this the installation on the communication site with the forms set to classic (in Settings the checkbox "Use Modern UI" in not checked). The classic style navigation is no problem for us, but the installation is not as responsive as it use to and sometimes it gives errors or does not save a comment.
Therfor we want to start with a new installation on a newly created Team site. But we want to keep al our existing data and functionality.
We also have the Asset list in our installation which has been build an installed by LocaTech. This is also in our new installation allready made by them.
They can help us with the migration offcourse but we wanted to know if there is a easier way to migrate with keeping all functionality and also because the method of saving each list as a template is not completely possibly at this moment because Microsoft decreased the limit of content items that can be saved as a template (due to Covid19). So that method does not migrate all our content.
We are currently investigating the ShareGate option as you suggested.