Wait for S Pen Support
One of the Galaxy Note series' most prominent features, the S Pen stylus, will be compatible with the Galaxy S21 series.
According to Ice Universe, S Pen support is 100% confirmed for the high-end Galaxy S21 Ultra. He doesn't mention other models so the stylus might be exclusive to the Ultra.
A report from Korea IT News backs these claims up. The site claims Samsung will bring S Pen support to the "Galaxy S21 series." The publication also claims that Samsung's "placed orders for digitizers, which are a key component in implementing pen input option."
Evidence has also surfaced over at German site Winfuture. The site says retailers are already listing Galaxy S21 Ultra accessories meant for the stylus.
Instead of a built-in slot to house the S Pen, Samsung's reportedly developed a special case that will incorporate a slot for the stylus.
Korean site Naver claims Samsung will sell the S Pen as a separate accessory meaning it probably won't be bundled with the Galaxy S21 Ultra.
Samsung itself has all but confirmed this news in a press release from TM Roh who is Samsung Electronics' President and Head of Mobile Communications Business.
Roh says the company has "been paying attention to people’s favorite aspects of the Galaxy Note experience and are excited to add some of its most well-loved features to other devices in our lineup." So while he doesn't call the S Pen out by name, he's certainly alluding to it.
A recent FCC filing for the Galaxy S21 Ultra also points to support for the S Pen.
If you're interested in pairing the S Pen with a Galaxy S you should hang around and wait for the Galaxy S21 Ultra.