First, just to be clear because codec terminology can be weird, x264 is a h264 encoder, not a separate codec. H265 is not an open standard so it may not play back properly if you use a Firefox or a Firefox based browser. I would recommend av1 if you can encode it, as it is good for quality and file size, however only new GPUs can encode it. CPUs can encode it slowly, but if you don’t have a new gpu (like 40 series Nvidia, arc, or AMD 7000 and maybe 6000) I would recommend vp9. It is a bit worse for file size but it won’t take a year to encode and should be compatible with most browsers.