This is what I see:
I use QTTabBar, maybe that's why.
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One of the previews is when you hold the mousecursor over a file. This will only show up with .txt files though. In QTTabBar, this can be disabled by going to the options, tab
Misc., and then uncheck
Show Preview tooltip.
Do note, there are 2 options with the same name. The bottom one is for sub folder information. You need to uncheck the top one.