Best way to mount towel bar to drywall

The towel bar originally installed by the builder 3 years ago finally wiggled its way out of the drywall. Looking at how it’s attached there are just two plastic mounting brackets the bar gets attached to and these mounting brackets are secured to the wall with a single small diameter screw/bolt. They originally mounted these to the drywall with plastic screw in anchors that the screw then got screwed into.
(Of course going directly into a stud would be best but the bar is 24" and the studs are spaced 16")
Is a better more secure option a toggle bolt along with a split/lock washer?

Yeah, I thought toggle bolt as soon as I read the post title. As for split/lock washers, I’ve heard they don’t really work that well-- the ‘springy’ locking effect fatigues out quickly and it just becomes a normal washer. YMMV.

They make heavier duty screw in anchors for dry wall

The toggle bolts are good as are winged plastic drywall anchors. Split/lock washer not needed.

One other option, put a mounting board across two studs that will then let you secure the towel bar too. So a ¼" 26" board of poplar or something can look very nice. Easy to pick up in a building store. Paint or stain appropriately.

I cut out the drywall where the towel hanger mounts and install wood the same thickness as the drywall and then refinish to match the drywall. Not really that big of a job and well worth it.

I would use a Snap Toggle rather than a toggle bolt, because (1) they’re stronger, and (2) they require a smaller hole. The gigantic hole needed for a toggle bolt might be visible after mounting the towel bar, depending on the shape of the bar holder.

That looks more like what I’m looking for. Do they sell those along side the other at the big box stores?

I’ve never had any trouble finding snap toggles at Home Depot type places.

Oh, another advantage I forgot to mention – if you ever need to temporarily remove the bolt, the part of the snap toggle inside the wall doesn’t fall off and get lost like it does with a toggle bolt.

I’ve had success with these plastic butterfly hollow wall anchors.

Your wall already has a hole from the previous attempt. I prefer spackling it and installing the towel bar a inch higher or lower. Drill into fresh drywall. Follow the instructions and use the correct size bit. Install anchor and tighten the screw to spread the butterfly. Remove the screw and install towel bar plate.

I like this kind of drywall anchor. The anchor part remains in the drywall. The only downside is that it leaves quite a large hole if you remove it.

Toggler or snapToggle style are the best I’ve found besides having a stud in place.

If you are doing a grab bar, remember you cannot use any of these anchors. The only anchor approved for grab bars is the Moen Securemount system or bolted/screwed directly into studs.