Don't be a chump. Employment-at-will means being an asshole is both parties' negotiated default. It says so in your offer letter unless you're at the very highest levels. Now, I have personally extended the courtesy of a multi-month notice to a manager with whom there was genuine mutual respect. But generally speaking, if a company mistreats me the only reason I'll give any notice is because I think it will directly benefit me. For example, maybe it will help to get a better separation agreement.
Is that mercenary? Yes. Do I like it? No, not really. But in the USA where I live it's virtually universal policy with private employers.
But also don’t trust your employer. Require important stuff in writing and contracts, don’t expect your employer to give anything extra for hard work / overtime (unless it’s in contract), don’t rely on “promised” benefits or rely on your employer to do anything they don’t have to.
And also, if you get another offer which pays 200% after accepting, or one which requires you to quit immediately, you might want to break loyalty. IMO this should go both ways: the company and employer should expect the other party to “betray” them if there’s a huge bonus like that. In fact all of this goes both ways and company/employer should have a decent, “loyal” relationship to an extent, but never put too much trust into each other.
* the other exception is toxic workplaces where your boss is being an asshole to you. Although in that case you should be trying to leave ASAP