Phone usability issues after latest update; can I revert?

Unfortunately no it's not possible to downgrade ios,what you are now seeing is called liquid glass and it's part of the operating system so it cannot be turned off but it can be modified a bit,try some or all of these settings;

Reduce Transparency (Tone Down Effect): Settings > Accessibility > Display & Text Size > Reduce Transparency (ON). This makes menus/buttons more solid.

Or/and (Aggressive Method):

1. Enable Reduce Transparency (as above).
2. Go to Settings > Accessibility > Motion and turn on Reduce Motion.

No, it has never been possible to revert back to any iOS version. You can review the options here to tone down the effects you see.

Liquid Glass - Love It Or Hate It - It's … - Apple Community

According to Apple:

After a software update is installed for iOS, iPadOS, tvOS, watchOS, and visionOS, it cannot be downgraded to the previous version.

What you can do about this:

Open Settings ➢ Accessibility ➢ Display & Text Size, then toggle Reduce Transparency = on.

Also in Settings ➢ Accessibility ➢ Motion, then toggle Reduce Motion = on.

Also in Settings ➢ Display & Brightness ➢ Liquid Glass ➢ Tinted.

In addition, you can provide ⇢ Product Feedback.

If enough requests are made, your feedback might help with future development, like a toggle in the settings.

Good luck! 👋🏼😉

No