Using an Instant Pot (which is what cook time reflects), turn on Saute mode, slice onions into thin half moon slices and cook with olive oil. Stir every couple minutes, while gathering the rest of the ingredients, until starting to brown in places.
If using a slow cooker, plan about a 6 hr cook on high. Skip the saute portion of the first step, and simply dump all of the ingredients into the slow cooker, mix, and let cook. Instant Pot folks, dump the remaining ingredients into the cooker. Mix, lock lid on steam (not vent), and use the Manual setting to cook on High Pressure for 35 minutes.
After the Instant Pot has reached pressure and started counting down, or during the last half hour of slow cook, cook and prepare your mashed (or boiled) potatoes. I like to mash a mix of 1 part cauliflower to 2 parts potatoes, sometimes I mix some kale in too.
Once the Instant Pot cook time has finished, let natural release for at least 15 minutes, then quick release. Taste and adjust with more salt if needed. Serve the sauerkraut and ribs over your mash, grind on some fresh black pepper.