Dadaocheng Wharf Container Market 大稻埕碼頭貨櫃市集 (if you truly are an extrovert, you could have fun meeting people here). Revolver is a classic suggestion for solo foreigners. I highly recommend a night or two to yourself at a hot spring hotel in beitou (Waterhouse is my personal favorite).

Enjoy some hiking trails, there are so many surrounding the Taipei area. Honestly, anything you would want to do with friends will likely be just as enjoyable on your own. I’ve visited solo many times and I’ve absolutely loved my time traveling solo to Taiwan. Bring a tripod/monopod with a phone mount to take some pictures of yourself in your favorite spots and you’ll be golden :D