But still when I restore it, it will either revert back to W10 or 11. I guess no one knows what to expect here?
But I will shut it down at the first thing you see, which is to select your language. The new owner will set it up and log in with his own credentials.
This will depend on exactly what process you use.
There is the original laptop/desktop maker's factory restore, which would reinstall the original OS.
But there is also a simple Windows reset, which will essentially just reset/reinstall the current OS.
Both (or at least the Windows reset) will ask if you want to keep your files or not. Be aware that this is just a simple delete and not a secure erase. With a simple delete, the space is just marked as empty but the data is still there if you use the correct tools to inspect the drive space. This is what some of the others are referring to when advising to destroy the drive or use a secure erase program. I would expect that the secure erase program may well destroy the ability to reset or factory restore on the drive anyways though.
As for if Lenovo is any good... Depends on the model. Every brand makes some better models and some cheaper crappier ones. My family bought some very nice Lenovo laptops a few years back. No real complaint there. These were their higher end Legion series though and in a different price bracket. My opinion is that if you're shopping the lower end models, they're all going to be compromised in one way(s) or another. Doesn't really matter which brand. The question is if the compromises are a deal breaker for your use case or not.
If you like the features and specs of the Lenovo you picked up, and you're not finding it crippled with excessive adware and bloat, I'd say just stick with it.