It’s built like a retaining wall but it isn’t one. It’s just a wall of those construction blocks. I was thinking it might be best as a way tagged with barrier=block, but I’m not entirely satisfied with that.
IMO simply barrier=wall
you may add height=*, possibly estimated
material=concrete_block has been used about 600 times in OSM so could add this too
alternatively wall=concrete_block has been used almost 4000 times but the wall=* key mixes purpose and material which makes me not suggest it
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