The Arduino/ATmega should be (and often is) happy with 3V3 data coming in
VIH (voltage for an input high) min 0.7VCC
"Min" means the lowest value where the pin is guaranteed to be read as high
You didn't quite read the chart in Section 29 correctly
TXA TTL H Level VCC=3.3V 2.1V - 2.8V
Operation supply Voltage Min=3.2v Typ=3.3v Max=5v
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