This is so annyoing as to why we can’t add name and keep custom waypoints.
The other issue is if you make a mistake in a flight plan with a custom waypoint you have to delete the whole flightplan and start all over again as you can’t delete custom waypoints.
Surely it is not that hard to add a custom waypoint option where you can add custom waypoints and keep them and use them like you can VFR and other navaid waypoints?.
I have found a work around by saving the plan and using an XML editor but MSFS cost me 180 AUD and you should be able to have a custom waypoint for such expensive software