Hi there,
it's a very good question.
Resetting your PC to factory settings ( I assume you use Windows 10) isn't really that great and the files can still be recovered.
You need to wipe your hard drive multiple times in order to 100% make your data unrecoverable
I can provide you the iso file that you can burn with Rufus (free image to usb stick burning tool) of this software if you don't want to purchase it
When it comes to phone, then if it's an Android, then you can easily bypass the lockscreen but if it's an iOS device, update it to iOS beta, wipe it once and set it up with an password (not pin, not passcode+Touch/FaceID).
iOS beta seems to be very hard to crack for those FBI black boxes that basically put your iPhone into recovery mode and then try to guess the pass : P
If you plan to factory reset your phone, just make sure to set the phone up again (without google or Apple ID account) and set some alphabetic password and this will at least overwrite most of the recoverable files. Eventually fill the storage up with some crap like iso files.
Don't use Samsung Knox since Samsung is forced to decrypt the secure folder if the authorities request them to do that.
@Gromit-CTB, who is not here and I have heard nothing from :)
My question above - do ISP providers have the capability to trace where you have been online, even with VPN/Tor?
Yes, in most countries they do.
Tor is actually very secure if configured correctly
VPN providers save logs for 15-30days even if they claim that they don't.
A guy from Germany tested 4 VPN provider and purchased chemicals that are used to build a bomb and he got visited by the police 4 times, even that he didn't enter any personal informations and shipped the package to an non-existing address.