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you could universaly use a 'fallen scifi' setting as the setting. An ancient civilizations built the gates (and fell apart in ancient times, or show up in the story later). some worlds connecting to it 'went feral' and fell back to fantasy-esque midevil style sword slinging.

add extra-planar demony monsters that let magic seep in the world (for wizards, warlocks etc) and that will let you have gates that go to fantasy realms, scifi realms, victorian steampunk etc. Maybe each world has to obey a paradigm set for that dimension, locking out the high scifi from the high fantasy.

I say make it 'fallen scifi' the most because scifi can contain fantasyelements, but fantasy tends to loose it's Fantasy Feel when you have elements of scifi in it anywhere.