My iPhone storage is larger than my PC hard drive, so can’t backup via iTunes?

Hi, I’d like to backup my iPhone 13 Pro Max into iTunes, but it keeps failing stating that the amount of space on my hard drive isn’t sufficient. I’ve been researching this all night and have found that you can move your initial backup file to an external hard drive, and then backup to the external drive for future versions, but what happens if you are unable to do an initial backup in the first instance? Is there a workaround please?