I guess this forum population skews toward older demographics. Nonetheless we can consider many songs by Lana Del Rey (thanks to her we have the sub-genre sadcore). Summertime Sadness is an obvious early pick but not the only one. Generally beautiful singing and compositions across many albums. Also many artists she inspired.
Closer to home (mine anyway) we have some excruciatingly sad lo-fi from Lil Bo Weep, especially Sorry. As she's no longer with us I find her stuff way too sad to listen to lately.