It's... really not that hard.
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Uninstall the new app, download the old app from https://www.apkmirror.com/ (which is basically an archive of most apps downloadable from Google Play).
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Use an app like APK signer to change the app's "signature" so it doesn't automatically update.
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Install it.
It takes like 10 minutes at most.
I did exactly this with the Discord app last year when they suddenly changed the app's entire layout.