I know the safest pronoun to use in Japanese is always 私, but I like the sound of 僕 and want to know if it would be odd or stupid sounding for me to use it? I'm a teenage girl and a foreigner(obviously). If used only with friends casually, is it weird? I've seen this on the web before but opinions seem very mixed, and a lot is 5+ years old(it seems in my results it least) so I mostly just want opinions. Thanks for answering!
Basically, 僕 is for boys. If you didn't know this, don't use 僕.
However, according to one recent survey, 1.2% of female middle school students actually use 僕 (source). About 20 years ago when I was a middle school student, there was one (and only one) girl around me who was using 僕 on a daily basis for some reason. After that, I've met a few people who have gender dysphoria and are using 僕 (or 俺) despite their feminine appearance.
I'd recommend that you do not use 僕 unless you are very fluent in Japanese and know what you're really going to do. It is true that a few native female teenagers (in the real world) use 僕 quite naturally, but a foreign teenager girl using 僕 would almost certainly sound simply "incorrect."
In fiction, female users of 僕 are not so uncommon, and it's considered as one of the ways to characterize a person. This page has a long list of female characters who use 僕 in fiction. Many (but not all) of them are boyish, tomboyish, naive, or have some other outstanding characteristics.