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I ported this from Al132's No Default Auto-Jump which is MIT licensed and can be found at https://www.curseforge.com/minecraft/mc-mods/no-default-auto-jump it was really easy to port forward to 1.16.1. Al is a coding GOD.
What it does is on first run of a client where the mod exists, it turns off the autojump feature. The player can turn it back on later if they like.