You can see what LLSPs are fully booked for future dates even though you cannot yet buy them for that date and you do not see what times are available. However, you cannot check what LLMP attraction availability is like unless you can buy it.*
In
MDE, choose one of the Purchase
Lightning Lane options (they appear on different screens). It will have you choose a date. Choose a park. It will show you the prices for LLMP and LLSP in that park on that date,
unless one or more of them is sold out. If it is sold out, it will say "Currently Unavailable." To this point, it hasn't asked you who you are booking for and hasn't checked to see if you have a ticket and are eligible to buy. It does that on the next screen.
Don't feel so stupid. Several pages back in this thread, I was the one insisting I couldn't see what LLSPs were sold out on future dates.
*- as far as I know. Maybe there is a way to see LLMP availability for future dates that I haven't learned about yet.