I would like to wait till angComponent.gridApi does not have the value undefined.
I'm not sure, but I think the variable angComponent doesn't update.
cy.getAngularComponent(tableGrid).then((angComponent) => {
cy.get(angComponent.gridApi).should('not.contain', undefined);
});
If you think the variable angComponent does not update, you should change .then() to .should(). Cypress will retry it for you.
cy.getAngularComponent(tableGrid)
.should((angComponent) => {
expect(angComponent.val()).not.to.eq('')
})