Additional SQL Server features and topics not covered by specific categories
I agree with Tom, install a newer version of SSMS from here: https://learn.microsoft.com/en-us/sql/ssms/download-sql-server-management-studio-ssms. (And since it is a new major version, it will be a side-by-side install.)
As Tom says, blocking can be a reason. On my web site you find beta_lockinfo that shows you current activity including blocking. Here you can see if you are being blocked - or SSMS is simply running a query that runs "forever".
If this database has over 100000 tables, I can see that SSMS gets more than a mouthful when it tries to open the view designer. While it is not my business, I will have to say that 100000 tables sounds like something is wrong to me. In a relational database a table is supposed to model a unique entity, and 100000 entities? That's a whole lot. One system I've worked with for many years has around 1800 tables - and I would call that a lot.
Anyway, you don't have to use the view designer, but you can create a view directly in a query window. I would even recommend that over using the view designer, which sometimes frowns on perfectly valid SQL.