Actually today I learned that many products, not just washing up liquid, contain salt and that's not the reason to not use washing up liquid but i cannot recall the reason why you shouldn't, so i don't. I hope that long convoluted sentence made sense, I'm not gonna write it again.
Anyway, what do I use? Uhm, I have various Muc Off products. TBH IDK what's what any more, i just plonk some stuff on and then rinse it off. Sometimes I even use a sponge on the frame but that's rare these days. I havent ridden my good bikes for a long time and of course they will get better treatment.
What I do rather enjoy is taking my filthy mud and crap MTB to the gas station and using their jet wash. It has a lance and a foam brush and a bunch of different buttons such as Foam Wash, Pressure Wax, Rinse the Wax, Pressure Wash, Final Rinse. I just whack in a couple of quid and go through the buttons starting at the top. Just ensure no water is sprayed directly into the parts where the bearings are. Then I get home and put on some chain lube.