Why does no windows appear when I open Apple Mail on MacBook Air?

It's an odd one that's been happening for many months, and it's annoying me enough to finally look for a fix.

No windows appear when I open Apple Mail.

While still active, I switch apps (command-tab) and return, and then everything is fine, but I shouldn't have to do that.

What's a solid and long-term fix for this please? I have seen threads from several years ago from other users, and so Apple needs to see this and take care of it.

Most up-to-date OSX: Sequoia 15.4.1

Thanks in advance.

[Re-Titled by Moderator]