Neo4j employs logical deletes to remove data from the database, optimizing performance and scalability.
Instead of physically deleting records, Neo4j marks them as unavailable by flipping a bit.
The IDs of these deleted (but reusable) records are stored, similar to a recycle bin.
 

Consequently, if you delete a significant amount of data, you might observe a slight increase in storage.
This happens because:

• The system needs to retain information about deleted records.
• Deletions trigger index updates, which may alter index pages not modified since the last checkpoint. Typically, an index reuses a free page from its own freelist for these updates.

Please see other related articles here:

• How to wipe out / delete all the content in a Neo4j AuraDB Instance ?
• nodes deleted Vs. nodes physically delete from hard drive (Reclaim unused space)
• How to compact your database store in Neo4j Aura?
• Deleting large numbers of nodes.