is the trail ok for hiking in late June? any tips
That is hard to know for sure. The Sefinenfurka, the pass you cross between Griesalp and the upper Sefinental, is one of the higher passes on the Alpine Pass route, at 2600 meters. It is known for having snow lingering into July. You would be going up the steeper side, where there are wooden steps and a chain or rompe to hold onto, but the steps may be covered in snow. If they are, you can always backtrack down to Griesalp and take the postbus.