create a record for smtp, a record for pop, and a record for imap. aapanel shows "stmp" dont create that. On one of my server I have setup successfully . on another one of my server after setting up all entries I am still getting error. Also you are on cloudflare switch of cloudflare proxy when you are doing setup. switch on proxy again after setup it wont show failed to detect mx records. Thats how I setup.
Also different gmail users need to mark your email as not spam. thats how you will build your domain and ip reputation so next time they wont go to spam folder. This is the only way. Try googling it for that