Mail is Slow and lagging.

For a laptop you must mean OS . By latest update, you referring to OS 13 Ventura?

Mail is fast on our pre-M1 laptop and our M1 desktop, both running OS 13.

I have the same issue. Brand new M1 Ultra. Mail is PAINFULLY slow. Takes a full minute to load my inbox. Takes another minute to load sent mail or any other folder.

I've tried EVERYTHING, from reinstalling the OS to using CleanmyMac to starting in safemode to rebuilding the inbox to removing and re-adding the icloud accounts. Only happening on my desktop. My laptop mail is fine.

Seriously infuriating especially since Apple doesn't care about this pervasive issue. I will no longer use icloud for email, switching to Gmail and will have to use a browser for my email on my brand new $5,000 machine. Unbelievable.

Ditto - and I have put off buying any new Apple equipment until I see a resolution on this - it is such a fundamental tool for my work (online marketing) and like you, I have gone to Apple directly for help, a number of times over a year or so now, and the proposed soloutions are myopic and ineffectual.

The situation has been exacerbated since the introduction of Monterey, I have also tried CleanMyMac etc (no visible effect) - this needs attention and a failure to resolve these software issues means that Apple, despite their great marketing are slowly deteriorating to become a branded box maker and not a branded lifestyle tool.

Like you I am currently running one account on Google Mail and another on Zoho Mail - both are far far better and I guess the only hope now is that Apple will buy Zoho and give us that upgrade as a solution ...

'If I am focused on one email message and waiting for it to "appear" I can quit mail and instantly reopen mail and the message is there in full, graphics, everything. If I then scroll to the next message, it is blank. I repeat the process, close mail, reopen and viola there is the message in full."

Sort of the same here on a 2015 iMac running the latest OS. I can immediately see all the headings, but message fields are blank for a couple of minutes. I go browsing while waiting. If I need to peek at my messages immediately, I take a look at the Mail iOS app on my iPhone. I am due for a new iMac so maybe that will end the problem.

Using an iMac 2015 and running Monterey 12.6 and Apple email the header pops up immediately. Occasionally the body of the email message will come up in a few seconds, however now the body only appears intermittently when it appears at all. Usually it now starts blank and remains blank. Apple is completely unresponsive with a solution. What will work for me (at least for a while ...) is to right mouse click on the subdued forward or reverse arrow in the header's bottom border line. The sought message opens as the body of a blank forward message format almost instantly, however any embedded hyperlinks in the body can only be opened by right mouse clicking on the link, then clicking again on the menu command "Open Link". As I said, this is Apple's problem, not a user error, and Apple doesn't seem to be making any effort to work with us to resolve it or even contact us to explain why Apple isn't going to fix it.

"... I've tried EVERYTHING, from reinstalling the OS to using CleanmyMac to starting in safemode to rebuilding the inbox to removing and re-adding the icloud accounts..."

So I just tried CleanMyMacX (CMMX). I have used it every week for maybe ten years in its general Smart Scan mode, but had not tried its specific tools for Mail Attachments (under Cleanup) and Maintenance (under Speed). Today I used both of those tools, then looked and saw 8 emails in my Mail Inbox on the iPhone. I launched Mail on the iMac and expected to see those emails having the problem of headers with no messages visible for awhile. But instead, all the messages were immediately visible.

While writing this, Mail received 3 more emails, whole messages were also immediately visible.

CMMX is not well-regarded by some on this forum. I don't know why; perhaps it is identified with Mac Cleaner which evidently does have problems. After ten years, and now this apparent success against the Mail problem, I am even more impressed with CMMX.

Same here on being able to see the message before it appears, by viewing it in Reply or Forward.

It is so very odd that it has been going on for months for everybody and Apple does nothing.