I didn't understand Cassandra/Scylla until I realized that it's basically a k/v store that lets you append data to existing keys. If your storage needs fit that domain, then I can vouch for Scylla being amazing to work with.
To put it in slightly more detail, it's a two-level data structure with two keys, a Dict[SortedList[Any]], to use Python type syntax. The top level key is also the sharding key.
Modern Cassandra is more like Dict[SortedList[Row]], where the row is basically a SQL row just like you’d expect in any SQL database