Dear Kato Kanachadze,
Good day!!
I understand your concern and I am sorry to convey that there is no out of the box feature to automatically hide the rows in the list when the status of the item in the column is changed to Completed.
I agree with you on having the ability to hide the rows In the list automatically when the item is completed will benefit the users and I suggest you to add your valuable idea as feedback in the SharePoint · Community (microsoft.com) which is the best place to share our ideas and improve the Microsoft products.
Moreover, as a workaround, you can create a new view in the List by the following settings:
Note: Progress in the above screenshot is name of the column that shows item is completed.
Open the List> Settings> List Settings> Scroll down to Views> Create View> Fill the details and at the filter select “Show items only when the following is true”> Set it as above> Enable the option “make it as default view”> Click OK to save the View.
If you don’t want to achieve your requirement via creating new view, I think you can achieve your requirement via custom Power Automate flow and I would like to suggest you give a shot by posting your concern in the Microsoft Power Automate Community - Power Platform Community to get the detailed help from the Power Automate experts on the possibility of your requirement.
Appreciate your patience and understanding. Have a great day!!
Best Regards,
Sophia