Oh wow, five years old! That's a fun age! Mine is 3 years old and yeah, while she has always been a fairly good eater, the tantrums and mood changes are real haha.
I think there could be many reasons why kids can be fussy about their food. For my little one, I've noticed it often coincides with teething or when she's going through a major development leap. Also, too much screen time can really throw off her eating mood and appetite so I try to ensure we have device-free mealtimes. As she's growing older, I'm also aware that her taste buds are developing and certain tastes or textures may be less appealing to her now than before. So yes, it's an ever-evolving situation!