NC v21 - is preview generator app still required?

Apologies for maybe dumb as, but with new release of NC v21, is Preview Generator?
Reason behind question is that release notes for NC v21 mention new, better handling of images preview.

At my end, I had pre-generated all previews with preview generator, but somehow feeling is that NC is not using it, as with the first entrance to a folder it takes quite a bit of time and resources to load it though with next it takes very little (even using different browser to avoid cached image files).

It is that either I don’t have everything set up correctly or the FIles (grid view) in image folders don’t use previews generated by Preview Generator.

It just takes enormous amount of time on Odroid-N2 to open a folder with i.e. 50 images for the first time. Apache processes are taking all CPUs, stacking up and almost exhausting memory. Further re-enter to folder takes very little time - hence feeling that something is odd.

These were my settings:

 'enable_previews' => true,
  'preview_max_x' => '2048',
  'preview_max_y' => '2048',
  'jpeg_quality' => '50',
  'enabledPreviewProviders' => 
  array (
    0 => 'OC\\Preview\\PNG',
    1 => 'OC\\Preview\\JPEG',
    2 => 'OC\\Preview\\GIF',
    3 => 'OC\\Preview\\HEIC',
    4 => 'OC\\Preview\\BMP',
    5 => 'OC\\Preview\\XBitmap',
    6 => 'OC\\Preview\\MP3',
    7 => 'OC\\Preview\\TXT',
    8 => 'OC\\Preview\\MarkDown',
    9 => 'OC\\Preview\\OpenDocument',
    10 => 'OC\\Preview\\Krita',

Maybe it is due to sizes set in config?

www-data@nextcloud:~/html$ ./occ config:app:get previewgenerator squareSizes
32 256
www-data@nextcloud:~/html$ ./occ config:app:get previewgenerator widthSizes
256 384
www-data@nextcloud:~/html$ ./occ config:app:get previewgenerator heightSizes

What are recommended sizes?


Did you fixed your problem?
In Nextcloud 22, the preview generator is even not supported?