I can only really comment about Kanto but i'd stay away from the following places Kawasaki, Shibuya, Akihabara (More white tourists but place is honestly just a tourist trap).
Now to change the pace I'm going to give some recommendations that the idiot influencers don't know about yet and you'll see no tourists.
Chichibu (Close to Saitama): Amazing onsens and ryokans almost entirely locals i didn't see a single foreigner. Really fresh water and clean air, the local food is i think the buck wheat noodles.
Hamamatsu (Shizouka): No foreigners, local food is Unagi it's delicious. A bit more of a city with some nice little shops for niche hobbies. The unagi is fantastic.
I'd like to hear other recommendations if anyone has any make the thread positive for a bit.
Kanazawa is rapidly booming this year for some reason.
Its hard to recommend less mainstream places to foreigners because the perspective is totally different from a japanese. majority of foreigns dont give a shit about onsen or ryokan or local food or outdoors stuff. japs travel to escape the concrete hell city that foreigners come to see. its not a bad thing to want to do that but i experienced too many times when more reserved (渋い) recommendations are disappointing to people who are on a once in a lifetime trip and dont want to waste hours on travel time and logistics
my personal favorites as a hiker who values natural beauty and history, split into tiers based on accessibility
easy tier - dont need car, next to big city or airport
kobe-himeji, hiroshima, kanazawa, kamakura-enoshima, nikko, hakone, fuji lakes, sapporo, hakodate, kagoshima
moderate tier - car recommended, 2 days minimum
aizuwakamatsu, nasu shiobara, oshima island, seto inland sea area, izu, southwest hokkaido, lake biwa, sendai
hard - significant project, youll need a car and a maybe a japanese friend
minami alps, tsumago juku and narai juku in nagano, anywhere in shikoku, noto and sado, mt myoko and tokagushi