System Data taking up too much iPhone storage.

Backup caused 77gb of system data so now i cant update to ios 18. Can I transfer my iphone 11 to iphone 16 without updating from ios 16 to 18?

I want to transfer my iphone 11 (ios 16.1) to my new iphone 16, so I thought it would be a good idea to backup and update it to ios 18 first. The backup took about an hour, but my system data jumped to 77gb, so now I can’t update. I’ve restarted my phone a few times, deleted the Safari cache and some photos/apps, but it won’t budge. It actually keeps increasing.

My question is: will there be an issue if I transfer my data without updating my old iphone to ios 18? I’m a bit scared to do a factory reset, so I’d appreciate any advice.

[Re-Titled by Moderator]