Welcome 😃
We're going to be looking at top coating options.
I am not endorsing and have not been paid by anyone for certain products. I will be as honest as I am... Even when I say, it may be the user - lol.

Supplies

Liquitex
Varathane
Zinsser
Rubber gloves

Step 1: Select Your Sheen

Although many artists like the look of resin, it could get expensive and let's face it, not many people actually like a super high gloss shine that is highly reflective.
Sprays like Krylon clear are non yellowing and if you apply light coats, it will produce a beautiful work of art.
Liquitex is expensive and well worth the price as a pour on or spreadable option. It goes on creamy and dries streak free clear! This product comes in satin to gloss.
I have tried the Varathane Diamond Wood Finish or Minwax Polyacrylic and cannot produce results without brush strokes. Today I am attempting to add zinsser latex extender to the Varathane, mix well to make a more pourable consistency. My plan is to then pour it on a painted canvas as a trial.

Step 2: Vividity

In this example, when colours pop with vividity, I am tempted to do the piece in Matt or semi gloss since it has many metallic paints already. It will help with longevity and against UV rays.