I see lots of potential for a legaltech startup that offers an easy way for companies and their employees to not have to deal with this and to compute tax implications beforehand.
What I've heard from people who have had to deal with this sort of thing is that you can outsource it to some degree but there can still be a fair bit of legal effort and cost. Especially for smaller companies, it's often just not worth the effort.
This is what Deel and Remote do for international employees. PEOs do this domestically (Justworks and Insperity, for instance)
Aren’t those Deel and Remote?
I think this is the reason umbrella companies exist. You invoice them and they make the appropriate deductions for tax and social security contributions.