How do you access your email account. Is it with a web browser or with an email client/app?
Where did you have the folders set up. Was it when you log onto your email account using a web browser or when you access your email using an email client or app?
I access e.mails via Edge and I have my email folders there when I open bt.com.
Not all folders are missing but sods law those that are missing are ones I use regularly