As john says, oak worktops look great, until you use them (also the same for highly polished granite worktops).
Eitherway, I would sugegst that as per Ikea text above yo ned to re-oil them.
I tend to use "Osmo 3032 - Clear Satin".
I use 400grade "wet and dry" sand paper (with water) to cut the old surface.
Let it dry.
Wipe it down to get rid of any dust.
And then two very thin coats of Osmo (I apply with a lint free cloth, or a paint brush and wipe down with a lint free cloth).
Key thing is always "THIN COATS" with Osmo.
I still get stains, water marks and hard to remove food (kids breakfast area!) - but with oak I (have to) consider it as a 'patina'.
The reason I like osmo (over varnish) is that if you get a skratch in it, simply wipe a new thin layer of osmo over it to hide it (it does not remove the scratch).
If bigger damage, sand the damaged aread and apply a coat of osmo in that area only.
Downside is that it is not varnish, so have to wipe off wet spllages and drips.
Osmo 3032 - Clear Satin
https://www.google.com/search?client=firefox-b-d&q=3032+-+Clear+Satin
SFK