So where it says support for 16 antennas, that means that there are 16 individual rf amplifiers, and the phase and amplitude of each channel is being set to do the beamforming?

Can a user just put in 16 rf feeds and do the beam steering themself?

If used in the standard form, can it do digital beamforming (send different info on different beams)?

Yes. Each PA probably has no more that 10 mW (assuming CMOS), but coherently added will yield over 100 mW EIRP. For RX the signal coherently adds, but the LNA for each channel has uncorrelated noise, so the RX SNR is not as good as a passive array (assuming zero feed loss). Probably other circuitry to keep all the channels calibrated.

No, not in that chip. It has differential I & Q baseband I/O which are split and converted using a LO coherent to all the channels, then amplitude and phase shifted.

No, that would require phase and amplitude weighting to be done at digital baseband. There are some other ICs with 4 channels to drive 4 element sub-arrays. These large MIMO arrays will have sub-arrays with RF amplitude and phase weighting, then each sub-array is fed with I & Q baseband with separate weighting.

With 22dBi they're quoting, it'd have to be all Tx or all Rx. Unless they're conflating amplifier gain in there, which sometimes happens.

The block diagram didn’t show a switch, and the NF is 6 dB, so I figured it was separate. I have used the HMC-6301, which has about the same NF. The switches get quite lossy at mmWave.