They're different for me as well. The pronunciation of duel, cruel, gruel, fuel, jewel etc. with /u(ː)l/ is a simplification of historical /-u(ː).əl/. This is not a feature of all accents, but I believe it's reasonably common. Wikipedia describes it under the broader category of "vile-vial merger," but I'm not sure if this is really a unified phenomenon. Unfortunately, the Wikipedia article doesn't seem to cite any scholarly articles that might give more insight into how prevalent this change is, or which words are most commonly affected.
What I've found is that I don't do this for words ending in -ual. So for me, dual and manual still have /-u(ː).əl/. I suspect this difference in my pronunciation is influenced by the difference in spelling: there are many other words where ue represents /uː/, such as glue, but I can't think of any words where ua represents /uː/. It can't be entirely due to some particular status for the suffix -al, since I pronounce real and ideal with /i(ː)l/; that said, I do use /i(ː).əl/ for some other adjectives ending in "eal" that are less common, such as periotoneal /perɪtəˈni.əl/ (from peritoneum perɪtəˈni.əm/).
There certainly are minimal pairs for people with either kind of accent. For people with an accent like yours, duel /d(j)u(ː)l/and dual /d(j)u(ː).əl/ are a minimal pair. For people with accents that always retain traditional /-uː.əl/, jewel /dʒuː.əl/ and joule /dʒuːl/ are a minimal pair. There may be other accents that merge all such words to /u(ː)l/ or /u(ː).əl/ without exception.