The following are the top five SharePoint related help and learning official sites:
SharePoint Help & Learning
https://support.microsoft.com/en-us/sharepoint
OneDrive Help & Learning
https://support.microsoft.com/en-us/onedrive
MS Teams Help & Learning
https://support.microsoft.com/en-us/teams
M365 Help & Learning
https://support.microsoft.com/en-us/microsoft-365
Microsoft Stream Help & Learning