Two Mac users reported those crashes to me, using Fabulously Optimized 3.2.5 (1.18.1):

https://bytebin.lucko.me/2es9UncZ3u
https://bytebin.lucko.me/M8gAYU8o0T

I do not yet know if it may be caused by a specific resource pack, but it might be worth knowing that the modpack enables the vanilla dark splash screen option.