Since a lot of people like a heads-up about how the end of the game works, you can read all about it here. Note that there are no spoilers at all, but the guide will talk about continuation options at the end of the game (hence the question at the very bottom). So come back later if you only want to know near the end.
Can you continue exploring your original Xenoblade Chronicles 3 file after your save?
Yes. After you finish the game, you'll have the opportunity to make a clear save file. Loading it up will bring you back to the area you were at before you finished the game. Clear save files will be denoted by a gold medallion in the top left corner of the file.
Just in case, you may want to save that clear file in a slot you aren't using (it doesn't really matter, but it might matter to you).
Xenoblade Chronicles 3 New Game+ carries over most of your progression
You can also opt to just play a completely new file and start the game over again. A new option will appear on the main menu right next to "New Game," for "New Game+."
Here is exactly what carries over, in the words of the game's own tutorial for NG+:
You'll retain your character growth.
All the tutorials you've read thus far will not come up again (but you can access them via the in-game menu).
All of your inventory outside of key items stay (but you will keep shards and nopon coins).
Unique monster kills will be reset (graves will revive, but if you clear them again you can see your original kill record).
Here is what doesn't carry over (and will need to be unlocked):