Unable to add custom template to a new modern site connected to a modern Hub

[Kateraid]

I am using a modern hub site collection in Office 365 Online & I am the 365 admin. I am trying to create a new site (within my hub collection) and want to use a custom site template and need help. 

At first I didn't have the option to upload a site template - under Site Settings>Web Designer Galleries, the Solutions option wasn't there. I used a PowerShell command to add this back in. So now I have uploaded my site template to the primary Hub site, but I can't find a way to use it for anything other than a sub-site. We're trying to avoid sub-sites (per Microsoft best practices). I typically create new sites for the hub using the SharePoint Admin Center - In the Active Sites window I click Create... but there's no option here to create a 365 Group site using a custom template. 

Are custom site templates only supported in hub collections if you build a sub-site? Does anyone know if there's a way to use a custom template with a modern hub site (not sub-site)? 

[#2 · Accepted solution]

Well folks, I answered my own question thru much trial and error, so I am posting what I did to fix this. 

1. Used SharePoint Admin center's classic experience to enable custom scripting at the tenant level
• This is not yet avail in the modern, so you have to switch back to classic temporarily for this
2. Used this PowerShell update to allow custom scripting on the Hub collection's primary landing site.
3. I used most of these instructions online to load the template and create the site       PMdevTestSiteCollection01.
4. After finishing the HOW TO CREATE A SHAREPOINT SITE COLLECTION FROM THE SITE TEMPLATE instructions, I switched back to the SharePoint Admin center's modern experience and edited the Hub site association to align it with my modern hub. 

This is a modern project site, connected to a hub collection in 365 online using the a custom template! Woo-hoo!!

The Hub navigation top bar is not on every page of the site, and the Quick Launch is being weird, closing menus inconsistently… but the bulk of the webparts that I wanted from the template have been applied. The page edit features seem to be a mixed bag of classic and modern, likely b/c the template was created in the classic experience.  I'm not sure there's a way to edit the Hub navigation easily in the new project site's landing page's interface. There is likely a way to do this in PowerShell or JavaScript I'm guessing. 

If I'm worried about security & leaving allowance for the custom scripting, I can turn all of that back off. At the tenant level I can do this in the SP Admin Center classic experience. At the site level I can run some PowerShell code to turn it off. I believe the custom scripting only needed to be enabled to allow the template to apply during site creation.

This is definitely connected to a modern Hub site collection according to the SP Admin Center. Parts of it feel classic and parts of it feel modern. It's like a hybrid site. I did some hub level searching on my Hub's landing page and it pulls data in search queries seamlessly out of the hybrid site. Some of the pages have a modern feel including the Hub top link navigation and the edit tools are modern.

This is definitely a site collection and not a sub-site, because /sites/ is in the URL

The only thing that's a bummer and I will have to research more is this hybrid site doesn't have an Office 365 Group alignment. I don't see an easy way to edit this. It might require Power Shell. 

@Kateraid