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You have to "burn" the ISO file onto the USB drive. Note this is not the same as using the file manager to take the ISO and just dump it into the USB drive. Make sure you select a drive where you're not storing anything highly important, because the "burn" operation destroys all existing data on that drive! On Windows you could use Rufus, Balena Etcher or such other program. I had bad experiences with Rufus but I cannot recommend something else better, somebody else will here eventually.
If you could still get into your old Linux Mint then you could take the ISO (copied to a different disk normally) then use "dd" terminal command to "burn" into the USB disk.
The trick is to make that USB drive bootable and to make an image of an operating system ready to be used in live mode.
After that is done then you have to boot from that USB disk. It wouldn't do any good if your computer boots from the internal disk. You have to go into the BIOS settings of your computer and change the boot order of the devices. Put "USB" or "external" or "removable" disk first of all, and "internal" disk last of all with "network" disk, or any option that appears like that. Save changes to BIOS and then reboot with the USB drive plugged in.
If you have an Hewlett-Packard laptop like I do, possibly one not built in these recent years, you could plug in the prepared USB disk, turn on the computer. Then as soon as there's any sign the screen comes on, press [ESC]. Wait a bit until it gives a message that it accepted that keypress then press [F9] or whatever key it tells you in a menu that it displays. This will bring you to a menu where you could choose how to boot. If you have a Sandisk USB disk then it might have the option to boot with EFI from there. Choose that; in many cases it will work. Otherwise you might have to go looking for the EFI file. Important: do not choose "OS Boot Manager" because that only boots into Windows.
Booting via "legacy" BIOS could be a pain if your computer has "secure boot" enabled, and there are other things to consider with computers being built in the last few years that might carry Windows11.