Does exist any way to add PS+ PS4 Collection games to PS4 without PS5?

I do not doubt that this is possible. It's very likely a real possibility to create such a device. PlayStation4 and PlayStation5 devices are effectively x86 PC's on the inside with a custom OS on them.

The fact that there's probably some buffer overflow somewhere that lets you run linux on the thing is in fact irrelevant. You 100% will not find any help on this site in doing so. That's because of legal issues. Consoles are locked down devices and the feature you're trying to emulate (the 'library' of games, or effectively your list of serial keys, within the console) on a regular PC is part of a copyright scheme.

If Sony sets in the terms of the product they're selling (the 'PS+ Collection') that in order to play the games on a PS4 you have to unlock that on a PS5, then you will need to own both consoles in order to play them on a PS4. Want to play on PS4 without also buying the other console? Then buy the games via other means.

Workaround: Loan a PS5

Since Playstation accounts are global internet accounts, and your games and owned products are not tied to your device, but rather the account, you can use a spare device to unlock them instead.

If you know someone who owns a PS5 (and who you can trust not to have done the above to their device) you can buy the product, login to your account on their device, add the games to your library, then log out. That would make them available on your PS4.