I found a temporary solution on reddit that may help until/if mojang fixes this issue.
A member by the name of WhateverTechBits replied with this:
I have found this problem as well. I checked the mojang bug fixing page suggested by @Lordofthevillagers and it said to access the option.txt file in the minecraft folder and "tweak" the option named mouseWheelsensitivity. Tweak. The mouseWheelsensitivity was set to 0.5. I put it to 20000. It now scrolls like 1.12.2 did. As a temporary solution, it works, but i still find it to be mildly annoying to go through all that hassle just to make it something that was already in the game.
I found a temporary solution on reddit that may help until/if mojang fixes this issue.
A member by the name of WhateverTechBits replied with this:
I have found this problem as well. I checked the mojang bug fixing page suggested by @Lordofthevillagers and it said to access the option.txt file in the minecraft folder and "tweak" the option named mouseWheelsensitivity. Tweak. The mouseWheelsensitivity was set to 0.5. I put it to 20000. It now scrolls like 1.12.2 did. As a temporary solution, it works, but i still find it to be mildly annoying to go through all that hassle just to make it something that was already in the game.
https://www.reddit.com/r/Minecraft/comments/7zk8lj/new_snapshot_scroll_wheel/
I think 20000 is still too low, and you may have to play around with it to get what you like. But it's something that might be a temporary solution.