Compared to its predecessor, x264 (AVC), x265 offers approximately 50% better compression at the same quality. However, it requires more computational power to decode.
If you want to watch Longlegs legally, check services like (rent/buy). The Blu-ray is also officially available. Longlegs.2024.1080p.10bit.BluRay.6CH.x265.HEVC-PSA