Can't remove stalled "inProgress" Time Machine backup
Don't remove that is my advice. Apple protects the Time Machine space from anyone making changes so you need to break those locks first, then you need to unlink every single file in that directory and then delete them.

The system is designed to reclaim that folder the next time a backup starts, so you aren't saving yourself any time and just doing what the system will do but slower.

I would make a decision - do you need the backups on that drive. If so, restart the Mac and then let it take a day or several to get the next backup set.

If not - set aside that drive and connect a new destination if you need a quick backup. Time Machine can handle multiple destinations so you can get your next backup done, then let it chew on fixing the interrupted one.

Or - wipe that drive using Disk Utility / remove all backups of that machine using the tmutil delete to remove the machine backup and not just one interval.

Since you're still learning of sudo - please don't use it unless you know you have a good backup and that backup isn't connected to the Mac when you run sudo and you have time to do a full erase of the OS and then full restore from your backup.

Once you're set with a good backup - here's the tutorial on sudo and sudo tmutil delete

How can I manually delete old backups to free space for Time Machine?