I just noticed announcement of new Fujifilm photo camera that can save images to HEIC/HEIF format with 10 bit depth:
"Support for HEIF image format
The HEIF image format delivers 10-bit image quality in files up to 30% smaller than standard JPEG files, continuing to expand Fujifilm’s reputation of deliverying high-quality images straight out of camera."
Similar explanations we can see for SONY cameras:
"Characteristics of HEIF format
When the camera records images in the HEIF format, they have the same image quality as JPEG images, but require a smaller file sizes since the HEIF compression efficiency is about twice higher than that of JPEG. As a result, the camera can save and transmit data very efficiently.
The HEIF format enables recording images with a rich 10-bit color depth gradation expression and is effective for reproducing gradations of the sky where the tones tend to change smoothly."
So i checked some random HEIC/HEIF online examples and they all opened as 8 bit in PhotoLine. Also in PhotoLine i try to export 16 bit document to HEIC format and open it in PhotoLine again. And it also was opened as 8 bit only.
So here is a small request:
Option to import HEIC format as real 10 or 12 bit (up-converted to 16 bit)
Option to export HEIC format as 8 or 10 or 12 bit
P.S. Seems imagemagick had same limitation in past but they fix the problem in 2020:
"The latest imagemagick release fixes the bug so these files are now correctly identified as 10 or 12 bit as appropriate."

UPDATE: Some explanation from Developers about macOS and about possible usage of libheif
https://github.com/strukturag/libheif
"On macOS, we are using the Apple libraries for importing HEIC and these libraries deliver only 8 bit with 10 bit images. I have already filed a bug report with a sample project about half a year ago, but I wouldn't hold my breath for a fix. If they fix it, it will probably only be in macOS 13."
"HEIC has patent issues, and we are not open source, so we additionally have license issues and are not allowed to use libheif for export and only with restrictions for import.
For us using the Apple libraries is the only reasonable way of supporting HEIC.
Martin"