Introduction
Recently faced one issue where Create Order button was missing from Quote entity form in one of the sandbox environment, I am going to provide step here how I fixed it.

Details
When we faced this issue in Sandbox environment, first thing I checked if it is available in production or not, and it was there, next thing I checked if there is any difference in the solution list. But I was not able to find any difference in the solution list but yes there version was different. I thought of checking if there any difference in Ribbon customization so I started looking into definition of the ribbon button and tried to comparing Sandbox with Production.

So as required I create a custom solution and added quote entity in both the environments and started checking their definition. I compared all the rules one by one and there I found one rule enabled rule called QuoteIsActiveOrWon which was different in both the environments.
following difference:

In Sandbox it was like following:

But in the Production it was like following

So I setup a custom custom enabled rule in Sandbox environment and added it’s definition similar to Production. like below

After publishing my changes I was able to see this button in quote form.

Summary
Sometime buttons is not visible due to some rule, so we can check it’s definition to make sure there is no rule which is hiding it.

Hope it will help someone!
Keep learning, Keep sharing !!