... local tax laws.

My current employer (100k+ company) says: "All miles/points earned on travel paid by the company needs to be spend on business related travel, e.g. upgrades, free flights or free stays".

It is not enforced is, they just make the statement for the tax authorities since in some countries those miles/points would be regarded as income. In reality nobody cares as it is close to impossible to audit

They make it hard to earn miles/points in the first place with a company credit card you have to use and special corporate fares/room rates which do not earn miles/points but it is still possible if you know you're way around.

Pretty painful since from my last job I was used to rack millions of miles and saw them as some decent compensation for all those hours in a Y seat and nights in hotels at the end of the world. Anyway, can't complain in principle as the new job is paid way better and easily covers the extra income through miles in an easier to use currency