A common misconception is that medieval people and earlier bathed rarely. That is false. They bathed often, daily or more than once a day, like people in advanced countries do now. They just rarely submerged themselves in water due to both the size of tubs and the fear of making it easier to get sick. Since back then, if you got sick it had a good chance of killing you so obviously sitting in water fully and getting out, especially in cold climates like Europe, would be moronic. Much like how people generally don't know that medieval and earlier civilizations commonly had sewage systems and water networks. Many ancient cities even had a form of air-conditioning using an excellent understanding of how geometry affects air pressure and even had running water in their homes. In short, how isekai manga often present medieval worlds is actually not all that inaccurate.
Yeah, honestly. I'm researching for a fic I'm writing, and many folks already had toilet paper even before 500 AD. The fall of Rome really messed up European bathing and toiletry habits since they apparently lost access and historical reference to plumbing systems, or didn't bother to install them when considering urban infrastructure (hence the occasional dumping of waste in the streets by 2nd and up-floor residents, even as late as the Victorian era, despite more modern plumbing existing by that point). Moreover, cultures that didn't use toilet paper already had pre-modern shower toilets and such. Not to mention the entire issue of air flow and cooling systems! They designed properties to accommodate air circulation naturally to keep the space to comfortable temperatures, especially in desert or hot climates (which makes the adoption of Western building methods as Top Tier a little disheartening, especially when they don't work for the area and require substantial HVAC system installations to be anything other than a hot oven).
...Ah, but enough of that. Medieval folks were a lot more intuitive and scientific than we think. It was just, well...wars, the Crusades, knowledge loss, poor information spread, the works. That's why I still mourn the loss of the Library of Alexandria, or any library, really. Who knows how much more advanced we would be if we spent less time burning books and knowledge just because of some sociopolitical scheme?