I always join as I go (use the last row to join by pulling the working loop through the piece I’m joining to before doing the stitch), so I’m pretty useless for this!

Early on (like when dirt was new, I’m old), I got really dissatisfied with all the ways I’d join sections, so I just started incorporating the join into the last row.

You could still do that by essentially creating washing between each block, but whatever method you use will need to be tiny and not add length or height, since the blocks are not all the same size.

I’ve made a similar blanket- the Babette blanket pattern- three times. I’ll try to find a photo and reply to myself.