Thanks for reply! Turn on/off "allow individual item checkboxes" is ineffective, take a look:
1. When is "allow individual item checkboxes" turn on - user is able to edit multiple items (rows) at the same time (default SharePoint edit form) - Attachment 1.PNG
2. When is "allow individual item checkboxes" turn off - user is able to edit multiple items (rows) at the same time (default SharePoint edit form) - Attachment 2.PNG
3. When 1 item is selected - customized form (PowerApps) displayed
The problem is that user is able to bypass the business logic set up in customized form (PowerApps) by simple trick when selects 2 items and click "edit". I'm looking for solution to avoid it - do not show edit/default form from screens 1. and 2..
Regards,
Maciej