I actually tried a bit more based on your comment and I found a way to fix my normal browser. Thank you for that!
Basically, I cleared all cookies related to smartthings.com and samsung.com. After that, I went to the regular https://graph-na04-useast2.api.smartthings.com URL, clicked to sign in, and it redirected to to login in https://us.account.samsung.com/[...]. I manually removed the “us.” from the URL, forcing it to go to account.samsung.com. After that, I can finally edit my devices without going to incognito!
For the shards, I didn’t know how that was called so I couldn’t find much information here. I guess now it makes sense and there’s no problem to stick with my -na04-. Thanks again @jkp.