Based on your wording - are you looking for scenery that actually is similar to Alaska OR a cruise that is something different than visiting the Bahamas, Mexico, etc…?
My take on AK cruises is that the environment is very refreshing and beautiful and that it offers a fairly port-intensive, excursion heavy experience.
Just recently I was reading that a big mistake is expecting a Norwegian fjords cruise to be a similar landscape. Biggest takeaway was the fjords themselves - that you spend a long time getting in/out of each fjord - and even one If the big cities (that one wasn’t even in a fjord).
Are you hoping to sail within sight if land as opposed to a lot of time with nothing but ocean?
Looking for a cooler temp (the crisp air of AK) v. the often hot/humid Caribbean?
If it is a vacation that offers excitement over just relaxing (making it more like a good vacation hotel base) - try to find an Itinerary that has few Sea Days. I would avoid a Transatlantic, Panama Canal or many of the Repositioning cruises.
I have had great experiences with an 11-night Med and an 8-night Southern Caribbean. Both had very few Sea Days (but those are needed if time in port is long - especially in the Med.
British Isles cruises are highly recommended (on my wish list). My sister and many Disney cruisers will suggest Princess cruises for these itineraries. If you don’t need Disney characters and decor, this can be a more economical way to cruise this area. Their ships are not so focused on bells and whistles, but provide a consistent level of service.
I find the best cruise similar to Alaska is another Alaskan cruise!

. We are booked for my 6th next Spring. I have not repeated ships nor itineraries. This next one is a 10-night, picked to include full days in each port we visit (several itineraries have late arrivals in one or more ports), including a full day (10am - midnight) in Victoria BC.
That stop is made to meet a US requirement for AK cruises RT out of Seattle. It is usually met by a 4-hour stop late night. Our day has enough time for a visit to Butchart Gardens and an Orca whale watch cruise - with hours left over.
A one-way cruise to/from AK can include some land vacation time in the Last Frontier. We did a 12-hour train ride from Anchorage to Fairbanks after a Northbound route.
I am definitely not discouraging a Norwegian Fjords cruise! It‘s another one if my dream cruises - and also not in Disney. Disney is my cruise home, but it suits my needs better if there will be a lot of time spent on the ship. Port-intensive: I would rather spend my money on excursions.
The next best similar option after Alaska is a land vacation In New Zealand!
Have fun with a lifetime of travel. So much to see!