Running shoes are not accurately sized at least not in uk as they get the conversion wrong sometimes from being made in different countries or they don't understand sizing
As an example a 42 jacket does not measure 42 it's made to fit someone 42 and is probably 44 inch + with a tape. Same should apply to shoes but they don't get it hense sizes all over plus they do conversation eg to UK USA wrong.
I'm a measured size 10 UK. For running shoes 10.5 is good as your feet swell running plus docks bit thicker. Adidas 10.5 fits me
I've worn up to 11.5 or 12 in other models though.
They just need to feel right forget that thumb stuff. Find model to suit your foot don't stick to one brand.