Do not waste your Resplendent Sparks crafting Mythic Enigma in Diablo 4
The Mythic version offers no stat advantage over the regular Enigma unless you are looking for an extremely niche endgame upgrade.
In Diablo 4 Season 15, we have this 1:1 Horadric Cube recipe that lets you turn any Unique you want into an identical Mythic version. And of course, you can still drop Mythic versions of any Unique. But what about the Diablo 2 Runewords? These uniques can only be crafted, so how do you get a Mythic version?
Well, you have to craft it too. Either you can use the Upgrade to Mythic recipe, or the 3:1 in hopes of getting a Mythic out of it. They can also randomly turn out as a Mythic directly when you first craft it.
Mythic Enigma Does Not Make Your Build Stronger
The problem is that it does not make your build any stronger. If you take Mythic 
Enigmafor example, it brings no upgrade at all compared to other Mythic items, so it would be a waste of 
Resplendent Spark to upgrade it.
Enigma is crafted in the Horadric Cube using 
Jah, 
Ith, and 
Ber runes with a Chest Armor base, it replaces your Evade with the Sorcerer's 
Teleport ability.
Its normal version gives you +2 to All Skills, 45% Movement Speed, 40% Maximum Life, and 12% Damage Reduction. Turning it Mythic does not improve those stats or make its Teleport effect stronger.
So spending additional resources just to turn it into a Mythic is just a waste of materials.
Is There Any Reason to Make Enigma Mythic?
There is one small exception. If you are looking for perfect Transfiguration upgrades, you can try to get Item Quality and keep the item modifiable. This lets you turn it into a Mythic, and it would max out the item quality transfigured.
And even then, depending on your build, it might be a really minor upgrade. This would be endgame min-maxing, and just getting the item to stay modifiable is a record on its own and might cost you a ton of resources that could be spent on an item that can really provide a huge boost.