Hi @Bikram Pal
Question 1: Do you want to protect worksheets? You may click Review > Manage Protection, turn on Protect Sheet.
Question 2: We can only set open worksheets via browser as default in SharePoint Library Settings > Advanced Settings.
Question 3: A workbook with macros can be opened on Excel online, but macros do not run in a browser window.
For more about features on Excel online, please refer to: Differences between using a workbook in the browser and in Excel
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
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.