disappearing emails

I have multiple email issues since upgrading to Big Sur -

Emails seem to work jut fine on my MacBook Pro (Apple chip edition), but those same emails into the same mailboxes accessed through my iPhone and iPad disappear. I see them land in the mailboxes on the phone and the iPad, but as soon as I try to look at them, they disappear. They do not disappear from my Big Sur MacBook Pro.

But, on the Macbook Pro with Big Sur, almost every email that comes in is labelled as Junk.

All this is new since Big Sur. Any ideas, anyone?

I'm also having multiple issues with Mail in Big Sur. Crazy things happening with my mailboxes- they move around, duplicate etc. etc. . Incoming mail going all over the place. Sent mail sits in drafts. [ not all , some ] etc. etc. Something wild happening with Mail in Big Sur. Today am calling support for the 2nd time. First time, lady thought the issue was with gmail. Not true.

Also this week, for no reason at all, my signatures list went haywire. Missing or changed signatures. Reversed back to old ones etc.

I'll try again with support again. Just wanted you to know you're not alone with this.

Why have all my emails disappeared in my email box

We'd need more info & best fo getting an answer if you start a new thread. :)

All my emails have just disappeared and it displays Read Only -

Generally when a Dive goes Read Only it's because of a failing Had Drive.

In Sys Prefs>Users & Groups, does it say admin under your name?

What kind of Account is it, POP, IMAP, Exchange??

In a Browser login to your WebMail, are they there on the Server?