When I encode something with complex fancy font subtitles I use these ffmpeg settings
-i inputfile -map 0 (other settings) -c:s copy -map 0:t? output.mkv
so for a real example these are my settings to compress a HUGE 25+GB anime down to only 2.3gb

-map 0 -c:v libx265 -preset medium -crf 22 -tune animation -vf "scale=-2:720:force_original_aspect_ratio=decrease" -c:a aac -b:a 448k -ar 48000 -c:s copy -map 0:t? 

audio bitrate should be lower but this anime had good music and was coming from a flac source so 448 is like 99.9% identical quality. dual audio would be more complicated, you could just copy the audio streams if it isn't flac which is HEUGE
preset slow will make the file slightly bigger but a lot better quality
also you gotta use mkv because it is one of the only containers that let you keep the complex subs
h264 is way better for compatibility though