Hey Thedrum13,
Thanks for using Apple Support Communities. We’re not aware of any current issues being able to change your Calendar alert tones and weren’t able to reproduce ourself, but we’d be happy to help out with ensuring it works as expected for you.
To clarify, you’re saying that the tone selected is not the one that plays at the time of the event or time set for the alert?
If you create a new test event, do you notice that the same behavior occurs? Also, make sure you’re running the latest software version, which is 16.4.1 (a).
For help updating your iPhone, check out these steps:
Update your iPhone or iPad wirelessly
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see more than one software update option available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.
For more info, check out: Update your iPhone or iPad - Apple Support
If you continue to have issues even with a new test event created in the Calendar app, it’d be best to contact Apple for further support: Get Support
Take care!