I recently received a suspected fraudulent email to my iCloud address. How can I secure may account?

Unique passwords, disable remote image loading in mail, don’t reply or opt-out, train the messages as junk, etc.

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

I suggest you learn about identifying scam/phishing attempts.

To be proactive, learn about phishing, scams, and Apple practices, etc., see:

If you see apple.com/bill, itunes.com/bill, or an unfamiliar charge on your statement https://support.apple.com/en-us/HT201382

Identify legitimate emails from the App Store or iTunes Store https://support.apple.com/en-us/HT201679

How to avoid scams when using Apple Pay to send and receive money https://support.apple.com/en-us/HT208226

This scam related information from Apple including reporting scams to Apple see Avoid phishing

emails, fake 'virus' alerts, phony support calls, and other scams https://support.apple.com/en-us/HT204759

How to identify scams related to purported apple notifications—per Eric Root.

“Apple will always address you by your name or the name they have on file for you, not Dear Customer, Dear Client or by using your e-mail address. The e-mail will be from @apple.com or @iTunes.com. E-mail addresses can be spoofed. You can go to Mail/View/Message/Show all Headers to see more. Apple emails won't have poor grammar/misspellings. Apple e-mails will never contain an attachment. Apple will never request personal information by email such as Social Security numbers, your Mother’s maiden name or full credit card numbers. …The only exception to the above I have noticed is if you order something from the Apple Store (apple.com), your receipt will be addressed to Dear Apple Customer. That is a receipt for a purchase you initiated.”

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And, see the Apple security documents:

If you think your Apple ID has been compromised https://support.apple.com/en-us/HT204145. From the link, among other things, Change your Apple ID password and choose a strong password.

Security and your Apple ID https://support.apple.com/en-us/HT201303

iCloud security overview  https://support.apple.com/en-us/HT202303

Ways to keep your information safe on Mac https://support.apple.com/en-gb/guide/mac-help/mh11402/mac

Using app-specific passwords https://support.apple.com/en-us/HT204397

Use Two-factor authentication for Apple ID https://support.apple.com/en-us/HT204915

Get help with security issues https://support.apple.com/en-us/HT201221

Send the e-mail to Apple as an attachment to a new e-mail before deleting it. You can forward as an attachment by going to Mail/Message/Forward as attachment. Or control - click on the email and select Forward as attachment. Make sure you send it as an attachment to a new email. If you just forward it, it will probably be rejected. You won’t receive a response.

reportphishing@apple.com

As with all such emails, ignore them, and in no way interact with the message or the sender.

I got an email concerning a purchase I did not make. Checked my account. No new recent purchase.