Mac OS Monterey - Apple Mail extremely slow tro open email text

Further to previous posts last year by other subscribers, I am still experiencing the issue with Apple Mail on my Imac (late 2015 Quad Core Intel I5 processor 8GB memory) whereby when highlighting an email in the inbox, the right hand pane shows the email and subject but no content. It could be many minutes before the content appears. This is only a proiblem on the IMac, my Iphone and Ipad both display content immediately. Additionally, I also use Mozilla Thunderbird as a means of sending bulk emails with merged data (something Apple has never offered) and this app displays the contents immediately. There is obviously something wrong with Apple Mail. I have tried other suggested fixes by turning off the privacy settings such as 'hide my URL' but to no avail. I would be interested to know if anyone else still has this problem or if there is a fix I am not aware of.