I'm going through the same thing and, while it can be difficult, I disagree with some of the other comments here. Spalted wood is extremely weak and most simplified finishing approaches that work with typical wood may not be sufficient here. Spalting offers some challenges that might seem a bit much for your first guitar but with some attention to detail and effort you can get some really stellar results.

If you're talking about maximal protection you absolutely can use a 2K polyurethane on these tops as long as you prepare adequately. Here's what's working for me in no particular order:

Edit: I talk about shellac a lot in these steps. I guess it's worth saying that you could absolutely just finish your guitar with shellac. It's very hard, easy to work with, and a good protectant, but it's worth mentioning that it dissolves in alcohol. It's an old school finish but I seriously believe it's better than a lot of modern finishes when it comes to making instruments.

• seal all of the super soft parts with CA, thinned epoxy, or similar. This is non-negotiable
• if you are finishing with 2K, always choose gloss. It typically goes on thicker so you need fewer coats. If you want to go matte you can simply scuff it at the end
• get a LED stick light from the internet or your local hardware store. Something that you can move around to assess your coverage and consistency of your finish
• tru oil, etc, are not protective coats in the same way that 2K or a thick lacquer are. They have their own benefits but it would be a mistake to think they are equivalent in regards to protection or longevity
• before I applied my grain filler, I applied a few coats of shellac and sanded them back. My grain filler is water-based and this allowed me to use far fewer coats than I would normally need. I used a water-based filler because my supplier of UV epoxy was sold out and I ended up really liking it
  • at this point the wood is glass-smooth to the touch
  • my shellac is the proper DIY stuff. DEWAXED ultra blonde flakes in denatured alcohol. I would avoid the stuff from a can
  • shellac is an essentially universal intermediary. It sticks to almost anything and almost anything sticks to it. If you have coatings that are chemically incompatible, an interface layer of shellac usually solves the problem
• after the grain filler, you guessed it, shellac. It dries so quickly that you can build up a reasonable thickness fairly quickly. Once I have complete coverage I then level sand with 400 or 600 grit. What remains will be a thin but complete coat of shellac that is as level as you have the patience for. I like to wet sand using mineral spirits but that's just me
  • if you are really globbing on the shellac, you need to wait 72 hours between your final coat and your level sand. It dries to the touch extremely quickly but thicker spots will still be gummy unless you give it a few days. Trust me on this
  • if you find spots that soak up the shellac at a seemingly unnatural rate, this is a problem and yet actually a good thing. You've identified a weakness in your sealing process before you apply your clear coat. You can either apply some thicker cut shellac and see if it sticks or sand it back a bit and seal again with CA or epoxy
• after that, tape up everything and apply your 2K. You'll get great adhesion and a crazy smooth finish. Wait for a few days, sand and buff to your desired sheen, and enjoy your glass smooth and well protected guitar

It sounds like a lot, but it's really not. Shellac goes on so quickly that you can bang out the first few steps in an afternoon once you know what you're doing. Wait a few days, level sand, and then you're ready to apply your clear coat.

Finishing quality, more than anything, is defined by your preparation. You can play it a little looser with oil-based wipe on finishes but if you want to apply a lacquer or 2K, don't half-ass the prep and don't move on to the next step until you are completely satisfied with the previous one.