I found Oracle's SQL Developer hard to setup, so I would like to use something easier, but with support of the same language or maximally close, preferably free (GNU) and preferably available for Linux.
Eclipse has various plugins, capable to develop Pl/SQL scripts, too.
Oracle SQL Developer uses an eclipse3 core, this is why it is not the best.
In addition to Eclipse, the other large mainstream Java IDEs are :
- NetBeans (open source, free of cost )
- Community edition (open source, free of cost)
- Ultimate edition (commercial product)
All three products are laden with features, are quite flexible, and come with a learning curve.
All three have their fans, and their advantages. NetBeans for example has the best integration of Maven. All three have special support for databases.
I suppose the "best" all around, in terms of the most devoted fans, is IntelliJ. The Ultimate edition has a "Database" plugin with all the power of their standalone DataGrip product for working with databases. Read the DataGrip documentation to learn about that plugin's features.
You do not give enough details in your Question to make a specific recommendation. I suggest you read some of the many blog posts comparing the products to guess which might be best suited to you.
Then budget some time to learn the product. None of them are simple and intuitive. Read their tutorials and documentation. Do some googling. Watch a few demo videos. You must develop some patience and discipline to learn gradually over time.
A good general-purpose alternative to Oracle SQL Developer is DbVisualizer (https://www.dbvis.com/).
The free version has some limitations (see the list here: https://www.dbvis.com/features/feature-list/), but the Pro (paid) version has Oracle-specific compatibility features. You can run standard SQL statements and PL/SQL blocks from the editor.
It's a Java-based desktop application, so will connect to anything that has a JDBC driver (and has special support for lots of specific database engines). And being Java based it runs on Linux.
The UI is clean and simple, and there are lots of helpful little features for working with data and queries. I've used it for a number of years and can't imagine doing serious database work without it.
It's worth paying for good tools, and I'd definitely recommend paying for the pro version if you're working with databases on a regular basis.