Tile coach has some pretty great videos where he tests the waterproofness of foam board vs membrane and membrane wins (albeit, marginally). The membrane waterproofing is thicker than the felt that comes preinstalled on the kerdi board. With all the requisite seam/corner/screw taping, I feel great peace of mind using membrane over concrete board, and it’s cheaper. However, for the ease of installation and ability to wet shim, kerdi board is a great option, it’s just very $$. For professionals who are trying to move quickly and save time, I think foam board is a great option. However for a DIY bathroom, you’re going to be going slow anyways, so why not save your money and get the best shot at waterproofing correctly (I emphasize correctly because there is a lot of room for error while installing your own membrane, so do your research). Remember, get the air bubbles out with a drywall knife, but don’t push all the thinset out, have the right trowel size, and overlap seams by 2”! More on reddit.com

First things first, you need to get a moisture test done to see whether or not there's actually a negative hydrostatic pressure (aka "rising damp") issue. If there is, you can explore options, but I'd recommend a proper epoxy based vapour barrier like Ardex's WPM300 if you're needing to seal the floor, but the absolute best option possible would be to fix the issues at the exterior before the moisture even gets in. Tl;dr eventual damage from higher moisture level sitting in the foundation causing erosion prematurely. Look at guttering/spouting, re-grading, exterior drainage, make sure it's all doing what it's meant to. Standard tiling waterproofing in this situation? Yeah nah, it's not designed for that mate, and it's utterly useless at the job you'd be trying to get it to do - it'll peel off the concrete because of the pressure building underneath it, it doesn't grab as well as proper vapour barrier membranes. That applies to both roll on membranes and sheet membranes. It's designed to keep water within where it's been painted on, and channel it down to a drain. Not to stop rising damp. As far as the whole crack isolation thing, if you've got shifting foundations then crack isolation membranes can only do so much to alleviate before failure sets in anyway. It's a band aid, not a proper fix. More on reddit.com

Where is laticrete hydroban ? More on reddit.com

Cement board by itself is not waterproof, it's the opposite. If you put down cement board you still have to waterproof it with liquid membrane or Sheet membrane. You can use sheet membrane over almost anything. I myself prefer Laticrete Hydro board. It's waterproof and very light. But very expensive due to material shortages right now. I know you can use Schluter Sheet membrane over drywall and Mapei makes sheet membrane also. I don't know if you can use just Laticrete sheet membrane on drywall you would have to go to there site. There is another company called Guru but supposedly it's popular in Europe but is sold in the states too. Sheet membrane is the bomb. I'm currently doing my Master bath using all Laticrete right now. More on reddit.com