Cetek16 :
I'm aware that pendrive can be defective, but HDD can fail too. So at this point it would seem that there's no good data storage. But i have an idea.
Since my internet is too slow to use cloud storage i want pendrive (256GB is more than enough, 128GB is not enough). But if i will have it already i could upload critical files to mega.nz. It's encrypted and safe enough. If my hardware or pendrive will be broken, i can download it from mega at any time.
For now i will look for something on google, but i have already made it before posting this. I will give links if someone in my situation will find this topic.
As long as you have a reasonably safe backup repository along the lines you have indicated there's certainly no impediment to your also utilizing a USB flash drive for backup purposes.
You've indicated that you require a flash drive with a capacity of not less than 256 GB. I've worked only with one that had this capacity, the Corsair 256GB Voyager GTX model. I had occasion to work with it for only a few months in 2016 and the item performed fine with high-speed transfer of data. (There's also a 500 GB model available but I've not had any experience with that model.)
One of the members of my computer club has been working with the SanDisk Extreme Pro 3.1 256 GB flash drive and apparently is quite satisfied with that component. (Don't be misled by the "3.1" designation. It's a Gen 1 spec and for all practical purposes it's a USB 3.0 component.)