My usual workflow is to create xmp files with LR+LRTimlapse and export final video file with AE from raw+xmp files. In version 7 I don't know how to save deflicker information to xmp file. Do I need to buy older version or is there another way?

LRTimelapse 7 supports the Visual Deflicker by default (which is the best one). Of course your workflow will still work, why don't you think so?

The old "simple deflicker" had been removed, but readded in 7.2 beta ( https://lrtimelapse.com/download/beta ), where you can find it on the toolbar above the table.