Why won't my toilet flush without holding the handle down for several second?

Because your flapper is flopping shut to fast.

First off, is it dual flush? ie. one for pee and one for poop?

For a traditional single flush:
Take the tank lid off to observe the flapper. There’s different kinds, but they all should open up far enough that there’s no flow obstruction for water going down the hole.

You might have to reattach the chain or you might have to replace the flapper which is a very simple and cheap job. There are Youtube videos of how to do it.

I most strongly suggest you go to YouTube and search for how-to videos on fixing toilets. I gaurantee there will be many of them and they will be more helpful, I think, than written suggestions, good though they may be. I LIVE by DIY videos.

I have found that when this happens the chain that pulls the flapper up is too long. Shorten it to the point where there is minimal slack.

Shorten the chain, just a little.

Yes, shorten the chain, but leave just enough length so that the flapper will fully close once the tank is emptied.

Thanks.

That didn’t do it. It’s been a long time since I’ve seen a toilet flush, but if I remember right, the pressure and bubbling is enough to keep the flapper up and open until the water is gone. That isn’t the case here. The flapper just floats down through the water and closes…..looking further.

Well, looking online, sounds like I need a new flapper, but I can’t imagine why. This flapper looks perfectly fine.
I’ll get one in the next couple of days and let you know.

You may have to position the chain so that it is more directly above the flapper. To work properly, when initially activated, the flapper will be at a 90 degree angle from it’s closed position. Then, as the water in the tank drains during the flush, the flapper slowly descends to it’s closed position.

Thanks, @kritiper. I’ll look at it again when I can.