How to create a sponsors logo block?
A proper way IMO is a “Sponsor” Entity content type with the Fields you need, then create as many Sponsors as you need. Then use Views to create a Block display and select all published Sponsor content and output it as needed. Then place the block in the desired region. Later you may want to expand on sponsors and add more structured data around them, which is why you'd have a content type (or custom entity type) over just a single-use block type.