The problem is simple : since the first 1.13 snapshot it is no longer possible to scroll between items while sneaking.
This problem seem to occur on macOS only.
Related issues
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bemoty
MC-124784
Unable to scroll while sneaking on macOS
Resolved
Duplicate
0
bemoty
migrated
(Unassigned)
Unconfirmed
Minecraft 18w05a
Retrieved
Thank you for your report!
However, this issue is a Duplicate of MC-121772.
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