Hi @Anonymous ,
Here is the complete notice:
Awareness: SharePoint Designer feature deprecation
MC210713, Stay Informed, Published date: Apr 25, 2020
We’ve identified an issue affecting SharePoint Designer
We’ve identified an issue affecting SharePoint Designer functionality for creating and editing custom Forms within SharePoint Online. After careful examination, we’ve determined that there is no known fix for this issue and have elected to disable the feature effective as of 3:00 AM UTC on Saturday, April 25, 2020.
Users who have previously leveraged SharePoint Designer to create custom Forms are instead able to utilize PowerApps for this purpose.
PowerApps is an easy and powerful tool that allows users operating in the SharePoint Online Modern experience to create and edit custom Forms for SharePoint lists and document libraries right from a browser window. PowerApps does not require traditional coding knowledge or any additional app downloads such as InfoPath.
*Note: SharePoint Online Classic users will need to temporarily switch to the Modern experience to access and utilize PowerApps; though, all custom Forms created in PowerApps are accessible by SharePoint Online Classic experience users.
As suggested by Microsoft, we can use Power Apps to customize SharePoint lists or library forms.
Reference:
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.