I like the .qgs format (which is basically a XML file), since I can quickly edit-replace it as a text document to bulk-update file paths/layer names. Also it is nicely usable with version control (github). Therefore whenever I can, I work only with the .qgs (vs. the compressed .qgz Container). So far I understood that I only need additional files in the .qgz if I'm making use of the auxiliary storage, which I learned here.
QGIS 3.28 apparently introduced a .db file in the .qgz container - called uOdkeP_styles.db in my case (where the first part is probably randomly generated).
The name suggests that this contains styles. This answer suggests the same. The current doc (also on github) isn't mentioning the .db. I also experience an (unusual) backwards incompatibility: QGIS projects saved with 3.28 won't be properly displayed in 3.16.11 (which I'm still using for some old plugins) - vector layers are all blue there. This speaks for styles being stored there and older QGIS versions not knowing about it being unable to read them.
BUT apparently the .db isn't needed for styles/symbology: To verify I deleted the ..._styles.db, leaving only the .qgs file. But all my layers still appear fully styled. Unlike the name/backward incompatibility suggest, the .qgs without .db is sufficient to correctly store (my) symbology.
However QGIS 3.28+ likes to have those .db files around: Exporting to QField (which creates a .qgs) or saving a .qgs creates instead an additonal [QGS-project-name]_attachments.zip that then contains one or more (for me probably "empty" 1KB) ...styles.db.
What do I need the ..._styles.db for? Is it "safe" to delete them, i.e. do I loose anything if I do?
