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Which is probably the case in the UK too.
from https://www.gov.uk/standard-visitor/visit-on-business
You cannot do paid or unpaid work ... as a self-employed person as a visitor.
It's my understanding that it is fine to travel[1] for business to go to meetings but you aren't supposed to sit down in your hotel and do other work tasks unrelated to that trip in your hotel in the evening. Of course it's very unlikely you will be caught, just as a self-employed person can sit in Starbucks while on holiday and send a few messages to clients.
[1] within the global north providing you are a citizen of the global north
I don't think the article is particularly clear https://archive.ph/jxTOL
I suspect, from the tone, it is talking about those who are self-employed, not a bit of remote working whilst on holiday.