Mac Mail
Mac Mail using current - OS Monterey 12.5 - OS. Open mail, click on Inbox on left, select an email and click - highlighting it. BUT, the text of the message will not appear for several minutes. "Main pane" shows the heading of the email (from/to) but not the text of the email. Been happening for several months, as has the spinning pinwheel - may take 10-20 seconds for for a webpage to load. Mac is 2015 model: perhaps internals going bad with time?
iMac 21.5″, macOS 12.5