[shiro]

You only get CPU Software upscaling options like Bilinear and Nearest Neighbour when Software decoding video content with Kodi.
By default AMLogic LibreELEC does NOT software decode.
It uses Hardware decoding and Hardware upscaling for everything OR...
Resolution switches 1080p <<-->> 4K to allow a 4K TV to do 1080p >> 4K picture upscaling.

AMLogic Hardware upscaling does not look blocky, it's just not quite as sharp looking vs what high quality software upscaling will do to SD content.
Nothing will fix low bitrate SD streams.

The only device with my custom version of LE Krypton I have doing 720/1080p <<-->> 4K auto resolution switching is the ODROID C2.
LE on an AMLogic S912 cannot even switch to a 720p video output mode. Lowest is 1080p.

Forget about all those high quality LE Intel CPU Software Kodi picture upscaling options like Bicubic, Lanczos3 etc that give you sharper SD quality picture outputs.
The best you can use is Nearest Neighbour when using LE AMLogic Software decoding for SD content, even that looks find for 720x576i OTA TV.

Thanks for reply. Those 480p videos what I am talking about are just some documentaries from WW2 or for simple view and delete...so picture quality ist not as important. But on the other side, I dont wanna something blocky like Doom 1 :-) Regarding what you said, it will be okay.
In the end, I will probably buy Vero 4k box, which is running their own ELEC-like distro on s905x chip as far as I know. I bet they have those things solved and there will be no problems...or can be some? :-)