HD works and 4K HDR does not: that is a bandwidth problem, and the usual suspect is the cable or a port. One of the few AV problems where the cheap fix is also the correct one.
Why it behaves this way: 4K HDR pushes far more data down the same HDMI cable than 1080p does. A cable that passes HD happily can fail at 4K rates. The signature is sparkles (white pixels flashing at random), black screens, or the picture appearing and vanishing. Nothing is broken; the cable simply cannot hold the signal together at that speed.
The order I check in:
Cables first. Use certified Premium High Speed or Ultra High Speed HDMI cables, and look for the certification label rather than the price tag. Certification matters far more than thickness or gold-plated anything. Plenty of expensive cables were sold before the standard they needed to meet existed.
Confirm the specific ports on both AVR and TV are full-bandwidth. On many models only some inputs support the full 4K HDR data rate; the manual says which. A perfectly good cable into a limited port produces exactly the same symptoms.
Enable the TV's per-input enhanced signal setting. Most brands ship this off, under names such as HDMI UHD Color, Enhanced Format, Deep Colour or Input Signal Plus. Until it is on, the TV tells the source it cannot accept the full-rate signal, and you get either downgraded picture or a handshake that fails.
Consider length. Runs of 5 metres and beyond are marginal at 4K with passive copper. If your source is in a cabinet and the projector is on the ceiling, that run is the prime suspect. Active or optical-fibre HDMI solves what thicker copper cannot, and it is the standard fix in every projector installation we do.
If you have replaced the cable, checked the ports and enabled the setting and it still sparkles, tell us the models and the run length. At that point the fault is usually a firmware update or a single mislabelled port, and one photo of the back panel resolves it.
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