Subfolders not showing in apple mail iphone 14 Pro iOS 16.5.1

Bailer-thanks for your detailed response. I did create parent folders and some subfolders under those. For example: created a parent called FINANCIAL. Under that I created subfolders such as Taxes and another called School Loans. They’ve all been working perfectly. Today I created a parent folder called MY HEALTH. I wanted to create subfolders called TKR and another called Fibromyalgia. The TKR subfolder went right into the MY HEALTH parent folder, but I cannot create a second subfolder for FIBROMYALGIA. It’s very frustrating because it works sometimes and doesn’t at other times. Is there perhaps a limit of how many parent or subfolders we can create? I deleted some older parent folders that were no longer useful, but that didn’t allow me to create the subfolders we’ve been discussing. BTW, none of my folders, either parent or child, were created in Gmail or on my laptop. All were created when I got my iPhone 14 Pro. I’m running iOS 16.5.1. But thanks everybody for your generosity and time.

Bruno: thanks for your input. Basically it’s a two fold problem.

1. I have tried to add a subfolder like MY SURGERY to a parent folder called MY HEALTH. When returning to my list of folders, the new subfolder does not show at all
2. I have tried saving the new email to the parent folder but it just goes directly to the parent folder. The gmail application I used at work never had this issue. Finally, I’ve been the family geek for too long to forget about rebooting the iphone. So many issues have been solved with that but not this one.