danir.de

The separable and non-separable kernels are fundamentally different:
 
Here is a (rough) analogy using Wolfram Alpha:
 
Non-Separable:
 
http://www.wolframalpha.com/input/?i=sinc%28hypot%28x%2Cy%29%29+between+-10+and+10
 
Separable:
 
http://www.wolframalpha.com/input/?i=2*sinc%28x%29*sinc%28y%29+between+-10+and+10
 
We include them both because separable is faster - and some people even prefer the results!
 
Hope this helps,
 
Andy.

@JDW. No... Sharpness is a separate parameter of the filter, regardless of mode...
 
You could have this:
 
Lanczos (non-separable; smooth)
Lanczos (non-separable; sharp)
Lanczos (non-separable; very sharp)
Lanczos (non-separable; extremely sharp)
Lanczos (separable; smooth)
Lanczos (separable; sharp)
Lanczos (separable; very sharp)
Lanczos (separable; extremely sharp)
  So it makes no sense to rename "non-separable" as "sharper".   I guess what the devs *could* do, is to throw away the slow non-separable version (why is it even there?!), and instead tweak the sharpness parameter of the faster separable version to provide both a smooth and a sharp version of the fast 1D implementation.   The sharpness of a Lanczos filter is defined by the number of "lobes".  
Further investigation showed that a Lanczos filter is fully separable, meaning that non-separable and separable are capable of identical output. The existence of the 10-15x slower "non-separable" mode means Affinity seem to have misimplemented Lanczos. There is no reason for the non-separable version of that filter to exist.
 
If all of this is correct, then it would be best to delete the non-separable (slow 2D version). Keep the separable (fast 1D version). Tweak the number of lobes to provide a few presets with varying sharpness, as such: http://avisynth.nl/index.php/Lanczos_lobs/taps
 
(Taps = affects the down/upscaling scale; Lobes = affects the sharpness; common values are 2 lobes = the best compromise between sharpness and low amount of ringing, and 4 lobes = more ringing but extra sharpness).
 
Why non-separable filters are slower: Upscaling in 1D only requires two 4-tap filters. Upscaling in 2D requires a single 16-tap (4*4 taps) filter, which is an order of magnitude slower. There is no reason to have a non-separable version of a Lanczos filter.

building for all distros can be a nightmare, would have to deal with what ever dependencies they have etc, i would rather they take the easy path and use flatpak so it runs on all distros and can be easily updated

I would do just Flatpak. There is no need to complicate things.

SreckoM - for start, perfect choice - for the record - complicated things it's consists of many simple ones.
Flatpak has rich Linux Desktop support and even ChromeOS
https://flatpak.org/setup/

In VfX Linux is mostly used platform. Apps like Nuke, MARI, Houdini are built on Linux than ported to other platforms. I worked in facilities with few hundred seats where 95% of them were Linux (which is same in most VfX facilities). We had several Win or OSX seats just for Adobe products (mostly PS for concept artists). For example, Weta, most of their workstations are Linux. If you want to work there as 3d artist, Linux knowledge is preferable skill.

Even automate whole process of making installable packages when new codebase will push on branch for Linux distro like Ubuntu, Fedora it's time one working Day using chat gpt3

Today thanks to Chat gpt3 moving codebase of affinity products in to any language rust, clang, swift, c++, you name it  and any os Fedora, Ubuntu, Etc it's just Time of several days to reach beta State.

I'm pretty disappointed in the lack of interest from Serif and won't upgrade as well. 🙁
I'm personally sad, because I like Affinity, but the problems with running unsupported via wine or by emulating are just too much...

kinda (really) mad that Serif isn't helping us much with running their softs on wine, like a lot of information about dependencies etc would help up so much.
I get the fact that they need to make a full version if they ever want to make it, and market it as linux compatible, and i assume that's why they aren't helping us at all.
I would also assume that they heard about linux users being 80+% of issues report when/if a company release a linux version of their soft.

But i also believe that there is a middle ground between the two and that they really should stop impeding help us, by giving us some helpful informations to make it run; or to make a wine fork for it if it really is necessary (so devs wouldn't have to retro engineer everything)

I know Serif doesn't owe it to us since it was never talked about anywhere (kinda mad about the "all platforms" v2 announcement hyperbole tho), but as it is with anything regarding Open-Source, it all comes down to morals.

PS: 
Thank you, genuinely, thank you to the few of you working on that.