Have you reported this? It's not normal.
Antivirus software can cause problems like this. So can network drives. MC can handle whatever the file system will.
Well, I've written something in another thread by another user a year ago:
https://yabb.jriver.com/interact/index.php/topic,127472.0.htmlThis was with version MC27 and I'm using MC28 only since yesterday (through MC29 license, since I skipped MC28), so I have not yet experienced any of the changes of the last year. My experience with a photo library with more than 1M files is much older (maybe around MC22) and was on an older quad-core CPU.
Still, when using the latest version of MC28, faster scrolling in some views stutters significantly when having "Show Fanned Thumbnails" enabled. This feature looks like it causes MC to load 5 times the amount of thumbnails. Not that I need that feature, but it indicates that I might get the same problem with a 5 times bigger library, while having it disabled.
I generally think that the way thumbnails are generated,stored and loaded should be reworked for both quality and performance reasons. For one there are newer compressions like webp available, which makes the thumbnails smaller on disk and in ram. It makes displaying them more expensive, but the amount displayed scales with monitor resolution and not with the number of files.
It might also make sense to provide more levels than just large, medium and small. Mip mapping usually goes down to 1 pixel. Currently MC sometimes uses the medium thumbnail and upscales it, instead of downscaling the large one. I only have a 1080p monitor, but I still notice that album and series cover thumbnails are not as crisp as they should be. If I scale the view to have 5 TV show covers in a row, the thumbnails are of low quality. If I change the scale of the view show only 4 in a row, they are as crisp as I would expect them to be. If I notice that on a 1080p monitor, it might look even more noticeable on a 4K monitor.
Last thing is loading. Usually the thumbnails are stored on the primary drive, which can be expected to be a SSD nowadays. Loading thumbnails from those large files requires a lot of random accesses. This is not a problem for SSDs, as long as drive queue is filled with lots of asynchronous requests, ideally from multiple threads. I don't know how thumbnail loading is done currently, but I expect a HDD optimized approach that loads files one after another, maybe in an optimized order. This would be worst case for an SSD since the queue depth and thread count would be both 1.
The quality of the thumbnails is currently the biggest downside of MC that I can think of. Performance is important too, but it is not that imminent. Improving the thumbnails would fix the first and substantially improve the second issue. It would also be quite important for image libraries. If I as a more technical person notice the problems in thumbnail quality, an artist or photographer will surely do so too.