How to copy a Document Library folder structure including Custom Columns and Default Values

Hi All, I would appreciate any advice you may have to help me with the following.

Overview:

I am trying to find the best solution to save a specific folder structure, along with its custom columns and default values so that it can be reused for each new project.

Background:
Our audio visual technology installation company has recently moved from using an on-prem file server to Modern SharePoint/M365.

To minimise workflow interruption and learning curves, our IT department copied all files to appropriately named sites/libraries in an arrangement which will be familiar to all users.

This is only meant to be temporary whilst we work out how we would like to use SharePoint and its associated apps.

Our company primarily works on a project by project basis, which means the first group of files and folders which need cleaning up are the set of Project Folders that we use repeatedly.

Traditionally, for each new project our Admin/Ops staff will start by copying a template of the Project Folder structure and rename it accordingly.

Over the years we have generated 000's of copies of the Project Folder template.

In principle this works well for us, and I have been able to replicate this nicely in Modern SharePoint. In case you're wondering; we don't want to change from folder structures to flat just yet as this would be too much of a change for the majority of our users, as most prefer to browse instead of search.

When it comes to searching for information during or after a project is completed, our users have regularly issues with finding exactly what they're after, and this is where I believe SharePoint document library metadata and custom columns with pre-defined default values can help enormously.

My first task:

Firstly, I am not an IT/software engineer, but I do have decades of experience using software like SharePoint and am not daunted by this task; in fact I'm finding it very interesting.
I have tried our IT depoartment, but their experience is really only around the initial deployment and ongoing support of SharePoint and do not have any specialists to advise on what is essentially user configuration.

It's now my task to define a new folder structure using to removed the old issues of file/folder duplication, mis-placed files, random naming conventions... i.e. all the issues typically found in a 10-15 year old on-prem setup.

I have setup a standalone document library as a project folder template with custom columns and default values. Only two of the folders have subfolders.

Note: many of our users would like more depth because it what they are used to, so to avoid this during the transition from deeply nested structures to flat, you'll see I am using a folder naming convention where I append the parent folder with a dash and the old subfolder name for now.

As a starting point you'll see in the image below that I have included several columns to allow for the wide variety of file types we deal with, but mostly to allow for the wide variety of search terms in use by our users.

My problem:

I have not found a method to copy this structure along with its custom columns and default values.

I first tried manual copy, but this not only doesn't copy any custom columns, it also leaves behind the subfolders. So this method is a fail.

I have been learning Power Automate and by following instructions found online have managed to setup a nice Flow which selects all folders (ignoring files) in the Project Folder template and copy the full structure to another site, i.e. emulating the creation of a new project.

But... no matter what I try, I cannot get the custom columns and associated default values to copy with the folder structure.

I'm also frustrated to learn that Modern SharePoint has had the option to create a Document Library template removed, as this would have suited this task perfectly.

Can anyone help?

FYI: here is an alternative view I'm planning on offering our users to help then get used to the idea of a flat file structure.

Thank you,

Craig