How can funnels be used as torches in Minecraft?

(See picture) How do you do that? You can't just light the funnel.

Yes, you can, with a plugin it will burn indefinitely.

What is a plugin?

Is it only available on servers, so that you can e.g. Do / lobby you also need a plugin

A kind of mod, but not every user has to install it

Server plugin, then everything burns indefinitely

Should go with setblock or WorldEdit.

With this you should be able to set a fire block, it will then continue to burn until there's some block update in the vicinity of the fire.

Mach / gamerule dofiretick false and it burns forever

You can with

/ gamerule doFireTick false

Turn off fire tick calculations. This means that fire blocks burn indefinitely, no matter which block. It also stops fire from spreading.

On servers this is of course solved with a simple plugin.

There's also a simple gamerule for that

Simply / gamerul doFireTick false and pack this command into a plugin and vola