SharePoint Online: Save List as Template Missing?

Problem:"Save List as Template" is missing in SharePoint Online modern sites!

Root Cause: We don't get "Save list as Template" link on list settings page in sites with custom script disabled. To enable save list as template in SharePoint Online, we should enable custom script for the site!

Solution: Enable Custom Scripting at SharePoint Admin Center and Site Collection Levels.

How to Enable Custom Script in SharePoint Online?
To allow custom script in SharePoint Online, follow these steps:

• Sign in to Office 365 and go to the SharePoint Online Admin Center.
• Click on Settings from the left navigation >> Scroll down to "Custom Script" section
• Under Custom Script section, Set "Allow users to run custom script on personal site" and "Allow users to run custom script on self-service created sites" options. 
  
• Click on "OK" to save your changes.

This enables custom script in SharePoint Online. However, this change may take up to 24 hours to reflect. To enable scripting on a particular site collection immediately, use this PowerShell script through SharePoint Online Management Shell.

Enable Custom Scripting at Site Collection Level:
Let's use PowerShell to fix save list as template missing in SharePoint Online issue.

#Variables for Admin Center & Site Collection URL
$AdminCenterURL = "https://crescent-admin.sharepoint.com/"
$SiteURL="https://crescent.sharepoint.com/Sites/marketing"

#Connect to SharePoint Online
Connect-SPOService -url $AdminCenterURL -Credential (Get-Credential)

#Disable DenyAddAndCustomizePages Flag
Set-SPOSite $SiteURL -DenyAddAndCustomizePages $False

This fixes the save list as template not available issue in SharePoint Online!

Instead of saving list as template and creating new list instances from it, You can also use How to Create a New List from an Existing List in SharePoint?