Floor presses skip the bottom third of the bench press range but train almost the same musculature. Plenty of strong benchers prefer them for triceps work anyway.
This is the whole mechanism, and it's refreshingly boring: RepRoute checks the equipment you ticked. No bench ticked, no bench exercises programmed. There's no clever substitution logic to explain — the lift simply never enters your plan, and the pattern gets filled by something you can do.
One thing to be explicit about: RepRoute does NOT treat a chair, ottoman or stability ball as a bench. There is no such mapping in the engine. If you press off a chair at home, that's a perfectly good idea — but it's your call, not something RepRoute knows about or plans around. Tick "bench" only if you own something you'd genuinely call a bench.
Standing pressing, push-up variations and pike push-ups keep upper-body pushing strong without a bench in sight.