This is what power users do. Buy a 4K Blu-ray disc (which you own forever), rip it using a drive like the MakeMKV compatible LG BP60NB10, and store it on a NAS (Network Attached Storage). You then stream that "Remux" to your house using Plex. This gives you the exact quality of KatMovieFix 4K but 100% legal.
Before downloading any "4K" file from KatmovieFix, check the file's Bitrate . A proper 4K file should have a bitrate of at least 15-20 Mbps. Anything lower is likely upscaled garbage. katmoviefix 4k