Hi @Ernest INGESBA ,
Welcome to Q&A forum!
First, please confirm that the following sharing settings are completed at the tenant level and site level:
Tenant level: https://learn.microsoft.com/en-us/sharepoint/turn-external-sharing-on-or-off
Site level: https://learn.microsoft.com/en-us/sharepoint/change-external-sharing-site
Then, confirm whether Check in\out is turned on. If it is on, please go to library settings to turn it off.
Finally, the permission setting is to protect information security. Although you can not set the link expiration time, it is recommended that you set it. Change links regularly.
Hope this helps.
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