The non-achievement world method (thank you VidGamiacUnlocked! Great video!)
Here are what the frog lights look like: https://minecraft.fandom.com/wiki/Froglight
You simply need to have one of each color variation in your inventory. (purple, green, yellow)
For the curious: "A tiny magma cube drops a froglight when it is killed by a frog. There are three colors of froglight that drop depending on what type of frog kills the magma cube: pearlescent (purple) from warm (white) frogs, verdant (green) from cold (green) frogs and ochre (yellow) from temperate (orange) frogs." (Minecraft wiki)
But the easiest way to get this is to use an achievement world.
There are a lot of options for achievements worlds. You can join a realm, download an achievement world, or join an achievement server.
I used both of the following worlds, one realm and one downloaded:
I was able to get this on The Button King's realm. https://open.minecraft.net/pocket/realms/invite/uZKDJV4SOpE
Personally, my favorite world is the Ultimate Achievement World. So easy to find what you are looking for. Here is updated version (1.19) https://drive.google.com/drive/folders/1kf1Ln_ejxexg3j6SFBGB...