I am trying to create a task list from a .stp file (sharepoint list template) that I saved and seems like is not possible, can someone help me....
After saving your list as a template, the template .stp file would be saved in the list template gallery: https://yoursite/_catalogs/lt/Forms/AllItems.aspx.
To create a list from this template, you just need to go to the site contents-> add an app. Search for your tempalte and choose it.
I assume your problem is you can't see where to upload the list template (.stp) cause in modern its not enabled by default.
So to allow it on a modern template you need to enable it. You first need to download the SharePoint online management Shell for PowerShell then run the ps snippet below
Import-Module Microsoft.Online.SharePoint.Powershell $tenantName = "yourTenantName" $SiteURL ="https://$($tenantName).sharepoint.com/sites/yoursite" Connect-SPOService -Url "https://$($tenantName)-admin.sharepoint.com" Set-SPOsite $SiteURL -DenyAddAndCustomizePages 0