Mail program keeps sending emails to spam

Hi all! I have a 2017 iMac running OS 11.4. About the time I updated to Big Sur (several months ago), my Apple Mail program started to (seemingly) randomly send emails to my spam folder. So I created a whitelist in my rules. But... emails still often go into the spam folder. I've called Apple support 3 times regarding this issue. I was told to try updating to OS 11.4, from the previous version... which I did. That didn't help. Finally, I spoke to an Apple person a couple of days ago. She said that just because I white list an email address, doesn't mean it won't be sent to a spam folder. It's searching the emails sent to me for triggers. So I need to tell my friends, family and clients and write so as to not set off these triggers (which are unknown and not specified anyway). WHAT??? I think whitelisting a specific email address should mean the program will send that email to my inbox NO MATTER WHAT. Am I wrong in thinking this is how it should work? I'm very frustrated, as I have to spend a lot of time now going through my spam folder to find all the emails that go thrown in there. It's a huge time suck. And I am often late in getting back to clients because I don't see their emails until many hours or days later. Has anyone else experienced this? Is there a more effective way to whitelist emails? Is there another program I could use that won't do this? I like having my email on my computer (as opposed to using gmail or yahoo or whatever). But it's becoming too annoying to use.