Since we don't know anything about your system, we can only offer speculations and tips for further troubleshooting.
Observed Deadlocks when executing queries from application in pre-prod but now on test.
I take that "now" is a typo for "not"?
One thing to check is to run SELECT * FROM sys.databases WHERE name = 'dbname' in both environments and check if there are any differences. Particularly, check is_read_committed_snapshot_on.
Apart from that, I would assume that query plans are different in the two environments. Slower queries are generally also more prone to cause deadlocks.
Assuming that you are on SQL 2016 or later, you should enable Query Store and re-run your tests, to see which are the top-resource consuming queries in the respective environments. It is also interesting to compare plans for the same query in different environment, to get a better understanding of what could be done to always be fast.