If I right click a table, I get the normal designer option:
But if I right click a memory optimized table, the designer is missing:
The server is 2016 and I've tried it in SSMS 16, 17, and 18.3. Is there just no designer support for memory optimized tables? I can usually drop and recreate the table when I need to make a change. That's what SSMS does anyway. But it's a pain in the ass when there are FKs involved.