I was running my Ridley with so-called 25mm Hutchinson Intensive tubeless tyres on 23mm (H Son Archetype) rims.
These measured less than 25mm across and easily fitted in the tight mudguards on the Ridley
When the front tyre gained a huge hole I switched the front to a 25mm Michelin Pro Race. Oddly however the mudguard did not fit. I removed the front mudguard It was only later when I measured the actual width of the Michellin on the H Son rim that I realised it was coming out as 28mm!
Recently I got some Schwalbe Pro One 23mm tubeless tyres, I fitted these and
measured the width, it came out as over 25mm
So don’t believe the hype