Yes, clownfish thrive in a tank without an anemone. In captivity they often host alternative substrates - leather corals, frogspawn, hammer coral, rock crevices, or even powerheads. Anemones are dramatic but they are also significantly harder to keep than the clownfish themselves. Most experienced reefers keep clownfish without anemones intentionally.
The clownfish-anemone partnership is iconic but it is not required. Captive-bred clownfish have spent generations in hatchery systems with no anemones, and they show no decline in health, color, or behavior when kept alone.
Anemones are demanding in ways clownfish are not. Bubble-tip anemones (BTAs) need stable parameters and high light, but they also wander - and a wandering anemone can sting the clownfish, sting other corals, or get sucked into a powerhead and shred itself across the tank, which is what happens 5-10% of the time. A magnificent anemone (Heteractis magnifica) needs a large, mature system; carpet anemones (Stichodactyla) eat fish; and even hardy long-tentacle anemones can crash without warning.
Wait at least 12 months from tank setup. Run stable parameters for 6 months before introducing one. Buy a captive-propagated bubble-tip anemone (BTA) from a reputable vendor, not a wild-caught magnificent. Cover any powerheads with sponge guards. Even with all this, accept that anemones are the highest-mortality piece of livestock you will keep.