Does Rick cover Malta in any of his travel books? If yes, which one?
Why not just get another book?
If you even need one--the tourism website was one of the more helpful ones I have ever used: https://www.visitmalta.com/en/
DK top 10 Malta; we have a whole shelf of DK pocket guides
Rick Steves guidebooks are unlikely to covers countries if he does not have tours that visit those places.
Rick doesn’t currently cover Malta (nor nearby Gozo) in any of his guidebooks. He’s added destinations and created new guidebooks, little by little, but his only Malta input, so far, is an 8-minute-long video from an “Island Hopping” TV pledge special several years ago. You can view the Malta video (and his other European island segments) here:
https://classroom.ricksteves.com/playlists/sRGVU
If you would like to spend a week on Malta, or divided between Malta and Gozo, here are a couple of options for walking and excursions with HF Holidays, a UK cooperative (non-members welcome on their holidays). You might get some ideas of what to see and do, or you might like to sign up for one. We enjoy their trips.
https://www.hfholidays.co.uk/holidays-and-tours/walking-in-malta-and-gozo?format=pdf&vid=3788
https://www.hfholidays.co.uk/holidays-and-tours/guided-walking-malta?format=pdf&vid=1402