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I'm one of those guys who liked to use Lanczos, but for the past 10 years swscale it's not working, and workarounds are to much hassle.
So I wonder, will this useless for now option will be removed or fixed?

Which program are you talking about ?


EDIT:
Topic moved from Coffee Corner

VLC of course.
There is option for software upscaling under filters tab, with quite a selection, but it seems since version 3 of the program, is left behind not working.

Could you post a screenshot of what you do to select your filter?

I can't find any lanczos filter exposed in the interface.

Menu Tools -> Preferences (Show Settings = ALL) -> Video -> Filters -> Swscale
Then on the right panel Lanczos is one of the available filters of Scaling Mode.

OK, thanks. Here are more details.

So this options (`--swscale-mode` in command line) defines the scaling mode whenever `swscale` is used.

When is it used? `swscale` is a "video converter", so it is used when the input and output format for a filter don't match for example. It is also used for subpictures (btw I found a bug while investigating: https://code.videolan.org/videolan/vlc/-/issues/25773).

So this option does not request to scale the video using that mode. Such a feature would not be easy to implement: it would require to insert `swscale` as a "video filter", but currently a filter produces an output picture from an input picture, it may not depend on the output size: the scaling is done by the vout (OpenGL for example). Moreover, it could only work with software decoding (so that the picture is available in main memory). And swscale is slow.

What?? are you sure? there is definitely a big difference when I change the scaling mode in swscale

If your system has GPU acceleration disabled or unavailable, yes. But on over 99% of systems running VLC, the swscale mode has no effects except for subtitles.