I’m wrong about cabotage being removed completely.
The EU-UK agreement allows two cabotage operations for foreign drivers per trip. It seems that this provision was put in place to stop Northern Irish hauliers going out of business (most NI hauliers operate extensively in the Republic, and vice versa). That’s better than nothing, but it does stop the pattern of self-employed long-distance drivers spending several days in their destination country doing short runs before tackling the long return trip. And like a lot of the EU-UK Trade Agreement, it’s a worse deal for the UK drivers, who might have to make those two jobs spread over nearly a thousand miles of return trip, as apposed to the the Spanish driver heading to the UK, who only can use his two jobs in the couple of hundred miles of journey within the UK, then take any number of jobs for the rest.