There are different ways of hiding the open button on the grid.
Prohibit opening records and inline editing
If you do not want your users to make any changes to the existing records or even expand the records using the child form, you can simply disable the Allow users to expand records setting. This will hide the open button, but also disable the inline editing functionality in this view. Therefore, your users will be unable to make any edits to the existing records. You can find this option by going to:
Your portal's or shared view's Tables section
Click on the table you'd like to change the button for
Views section
Click on the view you'd like to hide the open button for
Disable Allow users to expand records
Prohibit opening records, but still allow inline editing
Alternatively, if you do not want your users to open records with the child form, but still make edits using inline editing, you can set the label of the open button to a blank space. This way, the open button remains technically present, but is essentially invisible to the user. Inline editing will remain functional with this approach.
Prevent users from editing
If all you want to achieve is to not allow users to edit records, you can follow this article.