Absolute vs relational embeddings [R]

I've seen many posts saying that absolute positional embeddings work only on fixed sequence lengths... But theoretically if we look at the formulae, ( Positional encoding matrix using sinusoids ) we can process any number of time steps and dimensions..... So my question here is

1. Is this true ( Sequence lengths aspect ) ? If true why and if false why?
2. What are the advantages of using Relative positional embeddings over absolute??
3. Why are relative positional embeddings …

dimensions embeddings encoding look machinelearning matrix positional encoding process question relational true work