Wouldn’t it look better for propaganda reasons to have at least some opposing candidates?

Yes, that's why propaganda talk shows there always have a guest with a somewhat critical tone. Obviously that one always loses the debate.

Belarus just had a popular position candidate for presidential elections. When the results were shown it ended up in huge protests in the country, which very well might have removed Lukashenka from power. The reason they did not was Putin sending his troops to crush it.

If you have something similar in Russia today, you have the army fighting in Ukraine, the economy is in a dumpster fire, Ukraine and the West are going to help the protestors and there is nobody to march in and crush the protests. In addition to that the number of different armed groups in Russia has increased a lot and chances are some are unhappy with Putin. Wagner marched on Moscow after all.

So best choice is to not have an election at all. However that chance is gone now. Calling it off would make Putin look like he knows he would loose. So he has to fake it and the best way to do it is to have no actual competitor, who could win besides him.

Because if you make it too obvious you’ll have the fourth Russian revolution in the last 120 years.

October revolution in 1905 to remove a lot of power from the czars, one in 1917 to completely remove the czars from government, another in 1917 to put the Bolsheviks in power and lead to the Soviet Union. Who knows what would happen were the current populace to overthrow Putins sham democracy

No, presidential elections in Russia traditionally follows Snow White and the Seven Dwarfs plot where The Great Lider™ should look much better, much saner and much younger than everyone else.