How to implement connections?

Question

Database design

Hello!
I find it difficult to implement the following relationship:
1) Table blocks

• id
  
• title
  
• structure
  

2) Table Pages:

• id
  
• title
  

3) entities_blocks table

• id
  
• entity_type
  
• entity_id
  
• block_id
  

That is, a many-to-many polymorphic relationship is implemented between blocks and pages.
The goal is:
How to implement an attribute table for a pivot table?
That is, I want the blocks to have attributes, that is, something like this table

1. id
   
2. block_entity_id
   
3. key
   
4. value
   

(It is not an option to suggest making fields in the database for each key option, because they will be dynamic)