Tetris Effect: Connected

Easiest way I found to complete this is to build up as high as you can to the left, leaving a double space to the right. then once you're as high as you can get, use as many non-line peices as you can in the gap. You should be able to clear 10 lines in a row by stacking these peices. have a T peice held so you can clear down a line if you dont have an appropriate one coming down

completed in Effect Mode - Quick Play

I did this by building up 7 columns on the left and leaving 3 empty columns on the right, then when the left side was high, fill in the right side to clear one row at a time.

This video by Nockmss on Youtube was helpful: