Basically Amazon's Collection Sync is a broken implentation.
Also you are the mercy of wrong Sales / Marketing pages on Kindle ebooks for Series, Author and Title.
If you don't use WiFi you've only on device collection Management. The only thing you can do with a PC is copy files.
I don't count jailbroken because most users won't or can't (either they can't figure it, or don't know or the FW version means it can't anyway).
The reader GUI and User control via PC is worse than 10 years ago. Amazon seem to regard a Kindle as terminal that's simply caching the Website for off-line use. I've still got 3 Kindles and have bought eight for wider family and myself over the years. I seriously considered a Kindle Scribe and also the Fire tablet with pen. However while I still buy Kindle ebooks (so long as I can read them on any device I own), I won't subscribe to Prime, KU, borrow ebooks, audible or buy any Kindle or tablet from them now. They've lost the plot. It's not Publishers driving their mad control as they even encrypt titles that Publishers want DRM free if they are delivered by KFX.
No asking if you want a change on your Kindle, but they do it. Delayed action FW rollouts and inability to downgrade a FW is also abusive. Even most PCs with TPM and supplied with Win10 or Win11 let you roll back FW of BIOS etc as Vendors make mistakes. Even W10 & W11 you can make checkpoints and roll back borked updates.
Almost every Android device has a developer option enabled by repeatedly tapping "Build".
Kobo you can mostly go back to any FW done since the model was released.
Like Apple iOS walled garden with less control and quality.
