Hello, this is how I would go from here.
whole circuit boards or parts are not a good idea, not only are there many metals involved, but these parts can have places hard for the acid to reach, and this can mean that not all of the base metals dissolve, and if you did dissolve the valuable metals if there was any remaining metal, inside these parts, it can capture your gold.
stannous chloride is made from tin and HCl, (95% tin solder is what I use, from plumbing supply house), this will test your solution to see if any dissolved gold is in solution, a violet color will indicate gold is dissolved in solution.
For more details, search the forum stannous chloride test. Study, how to make and use it, it is your eyes to see gold in liquid.
If your solution tests positive add a clean piece of copper metal to cement gold as black powder, here we do this only if gold is in liquid.
If solution test negative remove the solution, (do not pour off, or disturb the powders) to a bucket to treat for waste, add iron metal to this bucket, later we will neutralize the acid, remove dangerous metals and dispose of salt.
For more details see dealing with waste in the safety section, to learn to dispose of these toxic waste solutions safely.
To me, in your picture, the rust looking material at the rim of your beaker, and the light blue color of solution makes me suspect Iron dissolved, the light blue resembles copper sulfate solution, I would be somewhat surprised if solution had any gold in it.
The powders, boil in HCL, dilute and rinse till water is clear, let powders settle in hot solution before removing washes or liquids, wash in boiling hot water till no more color.
And then wash in a solution of sodium hydroxide, to help remove chlorides, rinse several more times with water to remove salt water,.
Dry powders, crush to fine powder, we need to heat these powders, red hot, keep them crushed, and stir to let them get air in the heating process, but we do not want to melt them back into metal, just keep them glowing red hot for almost an hour, this will oxidize base metals, and remove traces of chlorides.
Let the powders cool and rinse them with boiling hot water, now I would go back to the step where you used nitric acid and start your process over, use dilute nitric till no more color is removed, any silver or palladium would dissolve in the nitric solution, it can be cemented out of the nitric acid with a clean copper buss bar metal.
Any powder remains after nitric, it could be gold, aqua regia would dissolve it as a yellow solution, use HCl, just add drops of nitric at once, let it react using heat, this way you do not add to much nitric acid to the aqua regia, also ridding the nitric acid works better, I do not recommend Urea, I heat (not boil) solution to evaporate, to a thick solution, add just a few drops of sulfuric acid (this helps if you heat too far, it helps to keep gold from making salts, and it will help to remove lead later), after aqua regia evaporated to thick solution add just a little HCl, not too much just enough to wet solution, evaporate again, HCL to wet again, again evaporate, this last time add 4 times as much water as solution, cover to keep out dirt and let sit overnight (silver and lead powder may appear as white salts, decant (remove solution from powders), now you can precipitate your gold if any with the chemical you would normally use.
Study Hokes book like we discussed, you can also search the forum for more information about what is said here, ask questions of things you do not understand, it is easy to answer a question, sometimes it is a lot of work to find gold in a mess.
If you had un-dissolved metals in the circuit’s boards or materials you first dissolved, your gold can also be trapped in them, and did you save them.
good luck, but do not just count on luck, (also study).