The easiest way to achieve this is to get change the datasource for the grid from microflow to association. This is usually doable but depends on the context in which you are using the grid.
What you can do is wrap the grid in a DataView feed by a microflow. In this dataview show a helperObject that is associated to all the objects you want to show in your grid. Then set the association as a data source for the grid. (helpfull tips, if you use a many to many association you can set the association value as a list, without having to loop over all the objects, also you can use a non-persistent object for this).
I would set the new helper object DS microflow to use respect entity context.
Hope this helps,
Another way to accomplish this in addition to Andrej's suggestion is to use the Data Grid Search Filters widget in the appstore, you can find it here: https://appstore.home.mendix.com/link/app/32075/Mendix/Data-Grid-Search-Filters
It should take you a few minutes to add it to your project and try it out - if it doesn't do what you want, you can easily remove it. I have found it to be a great addition to my toolbox regarding search in Mendix.
Also, I just checked and the latest release of this widget is version 7 compatible.