If I make a new Apple ID will I loose all my stuff from my old Apple ID?

Short answer, yes.

The long answer is complicated.

For items like contacts, calendars, and reminders you can sync them to a Mac or iOS devices, then turn off iCloud syncing. When you do so you’ll be given the option to save a copy on that device. That data can then be synced to your new AppleID.

For photos and documents you need to make sure it’s actually syncing the full original quality items to your device. If iCloud is helping manage storage, then the copy on the device my just be thumbnail or proxy. All of that can be checked in Settings.

For 3rd-party apps, you’d have to look at how that app handles data when you stop syncing to iCloud.

For any iTunes or App Store purchase, they will stay registered to your old AppleID.

You can try setting up Family Sharing between the IDs if you want to be able to share purchases made with the IDs.

Family Sharing

Family Sharing - Set up