IMO waterproofing butcher block is not a good idea. Wood has an enzyme that kills bacteria and if you use a water proofer that also keeps the enzyme from working . The counter in this kitchen is 18 yrs old I ran a catering biz from there for 8 yrs and all I did was ioled the area around the sink more often than the rest but you will notice the sink I used with its own drain board and not an undermount .

Thanks for your comment. I assume the enzyme is only important if I'm planning to use the counter top for food prep which I'm not. Thus, with an undermount sink isn't it very important to waterproof the area around the sink at minimum? The consensus seems to be that with an undermount sink mineral oil would be insufficient.

The waterlox original starts out very shiny, but it does dull some with time. However, Waterlox does have a satin product that you can use as the final coat. I haven’t tried the satin finish, but I’ve got walnut counters covered in Waterlox in my kitchen and two of our bathrooms, and the waterproof aspect has held up perfectly over the handful of years we’ve had it in our large family household. Here’s a photo of my kitchen fairly soon after it was completed.

We had butcher block with under mount sink in our house for over 10 years...never used anything but mineral oil..just wiped up water when needed...also ...butcher block is not usually porous wood...

True butcher block is end grain maple. Most wood counters being sold these days are not maple, or end grain. Most are edge grain or face grain. They are designed to be decorative, not used. Some of the low end stuff sold is more glue than wood. Buyer beware. Buyer beware about water and wood. I’d always do stone or stainless around the sink. Like Julia Child did.

You could consider Rubio monocoat. It has a lot of colors and basically no sheen. https://www.houzz.com/discussions/5919611/experiences-with-rubio-monocoat-for-kitchen-countertops

Those awful pictures are a display of poor maintenance more than any thing else..(as the surroundings suggest).... a little spritz fo clorox now and then would have easily stopped all that mold...i find my stone counters of today take more babying than the wood did...but i admit am meticulous about a clean kitchen...and only chose wood in our Aspen home as it was an old restored rustic cabin ...some people may choose it because it is also much cheaper than stone...

I can't speak to the edge grain part. We have black walnut island and counters made from boards. We used the countertop oil from Livos.

https://www.livosusa.com/

Starting with the bare wood we put on two coats. We had done a test on some spare pieces. The more coats you put on the shinier it will be. The two coats left a very matt finish that we love. On the island we have only done one more maintenance coat after 1 year. 3 years later we haven't had to do another although it is starting to look like soon would be good.

On the counter where the sink is we've done maintenance coats about every 9-11 months. We were a bit fussier with the sanding since it wears unevenly with the higher use around the sink. Important to be really skimpy with the recoats. We weren't paying enough attention on 1 of our maintenance coats and we used too much so it was much shiner. We just left it and it eventually was ok. We could have sanded it off but couldn't figure out why we'd do that.

We went with a top mount sink to minimize the water drips from the faucets and soap dispenser but I wish I'd gone with the undermount (it was our compromise with the guy doing the work. We had to talk him into the walnut so the top mount was the deal!)

Love the wood. Love the oil product If your island ever looks like the horrid pictures noted in other comments take the sink off, give it all a good sanding and start again. It's wood.

A better product for mold on wood is: Concrobium

After lots of research my niece used this stuff. She said it has been amazing.

Waterproofing is not key...or even needed...as i stated in my previous post as a result of having butcher block counters for over 20 years...in two different homes....only using mineral oil....with a thorough cleaning and new application of oil as needed

The mineral oil will sink in as it dries and have no sheen..only change is the color will darken slightly ...and will lighten up sooner if it gets more natural light...

This choice of countertop is definitely not for people who want a pristine finish...if it gets “used”... it gets more and more marks and scratches..imperfections

Around a sink I'd use a clear penetrating epoxy sealer. SystemThree makes a good product and it doesn't have a picture of a boat on the bottle so only costs half as much. (Still not cheap) Use steel wool, fine (600-2000 grit sandpaper, or scotchbrite pads to reduce the sheen to whatever level of flatness you want. It won't look as nice as an oil finish, but it will actually keep the water out, at least for a while. Be sure to thoroughly seal the edges and underside prior to installing the sink, then don't scratch through the surface while doing the installation.

The big issue is that the finishes that are shiny are the ones that bring out the grain and add depth. You can mattify the look, but the overall look will be dull and without depth. You don’t pay the big bucks for walnut to get a dull powdery look.

There's a tradeoff between depth and clarity and shine for sure. People pay the big bucks to do all kinds of odd things, this is far from the worst. A rubbed out finish can be clear, let the wood glow, but not have "new car" shine.