[hdmkv]

Don't think my Vizio can force HLG. Didn't save any clips, but found a raw DV sample here.

Maybe I should've kept the 12 as I'm now seeing videos uploaded to YT like this one that look great in HDR (HLG) when watching using Fire TV Stick & the Smart YouTube TV app. nVidia Shield TV doesn't support HLG, but via Smart YouTube TV, the clip still looks good in SDR. But, when I download the clip from YT using 4K Video Downloader (see MediaInfo below) and play it using Shield TV, I see the same overly bright & washed out picture as with the raw iPhone 12 samples.
 

Code:

General
Unique ID : 13160765428354171740915578229189883592 (0x9E6ABD54474B6A3DBA4B185BEE1B6C8)
Complete name : D:\Downloads\iPhone 12 Pro Max - 4K@60p 10 bit - HDR Dolby Vision.mkv
Format : Matroska
Format version : Version 4
File size : 449 MiB
Duration : 2 min 15 s
Overall bit rate : 27.7 Mb/s
Writing application : Lavf58.20.100
Writing library : Lavf58.20.100
ErrorDetectionType : Per level 1

Video
ID : 1
Format : VP9
HDR format : SMPTE ST 2086, HDR10 compatible
Codec ID : V_VP9
Duration : 2 min 15 s
Width : 3 840 pixels
Height : 2 160 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 59.030 FPS
Color space : YUV
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : HLG
Matrix coefficients : BT.2020 non-constant
Mastering display color primaries : Display P3
Mastering display luminance : min: 0.0050 cd/m2, max: 1000 cd/m2

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : A_AAC-2
Duration : 2 min 15 s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 44.1 kHz
Frame rate : 43.066 FPS (1024 SPF)
Compression mode : Lossy
Default : Yes
Forced : No