How can I level and secure retaining wall steps?
Trying to quick fix masonry in the pictured condition is most likely not the way to go. Remove the treads and rebuild the the footing under the riser with pea stone, backfill with sand or pea stone and replace the treads. Slanting them downward is not a good idea if you live in a place where water freezes in the winter. If you want to add adhesive between the riser and tread use liquid nails for masonry. I’ve done tons of block stairways, to last they need to be relaid.