Hi
On Form i add a Subgrid and in this subgrid i add a component Editable grid
The subgrid takes whole new section in the form and when i open this section the default opens editable view which i can switch to view only by selecting Show as-->Read Only Grid
Is it posible to make so that the default view of this subgrid is Read Only?
Unfortunately you cannot programmatically switch the grid type yourself (i.e. replicate the Show as button on the subgrid)
What you can do, though, is make each selected row readonly when the user has selected a row, so, even if they are using the editable grid type, you can disable the cells across the selected row using javascript
According to the documentation: https://docs.microsoft.com/en-us/power-apps/developer/model-driven-apps/clientapi/reference/grids/gridcontrol, you can only get the currently selected view (getViewSelector method) when the grid is a read-only grid, but the editable grid also contains this property and you can can get the currently selected view if the grid is an editable grid as well. I would suggest opening a support ticket to check whether their documentation is up-to-date (because part of the documentation on the link above has not been updated to reflect the latest information e.g. getGridType method from this link does not reflect the current latest information).
If according to their documentation, the information is the latest, then you can instead get the fetchxml of the current view (getFetchXml), and then use that xml to determine whether you want to lock the rows the user selects