@AmauryV When exporting for screens in Illustrator, the Prefix field in the "Export for Screens" panel is not linked to or saved with a specific file. It operates as a global setting that retains the last value used across all open Illustrator documents. Personally, I prefer this because it speeds my workflow. But it sounds from you, it's frustrating when working on separate projects simultaneously, as you have to manually change the prefix for each file.
The rest of the export settings, such as Artboard names, formats, and export folder, are tied to the individual file. These settings are stored within the document's metadata, allowing Illustrator to recall them when you reopen the file. The prefix is the sole exception to this rule.