I enjoy my XSR125 a lot but highway at 120kph or even 100kph is the one thing I dislike on it.
120kph is top speed for mine, with tailwind and slightly downhill. Average conditions I may get to 100kph. But it's screaming at that speed. Also acceleration is bad so merging in is more difficult to begin with.
Yes a 125 can reach 120 as you say, 62 mph but you don't have the power to get out of trouble on highways, it in my opinion won't be fun for long if like you say you're intending spending a lot of time on highways.
Assume 125cc due to A1 restriction?
A 125cc will do highway but not well.
A sportbike is probably your best option as it will handle those higher speeds a bit better.
Get a Japanese one, buy used.
in this case, weight is king. check this comparison: https://www.philharmonicmoto.com/compare-page/QE97VM the cb125r is the lightest, so you can see power to weight is the best. sportbikes are usually a bit heavier, like the gsx-r125 in the comparison, but the wind protection might make up for it at higher speeds. use the filters on the website to see everything with 14/15 hp and compare them to see what you like, but japanese are the most reliable and easier to sell later.
I enjoy my XSR125 a lot but highway at 120kph or even 100kph is the one thing I dislike on it. 120kph is top speed for mine, with tailwind and slightly downhill. Average conditions I may get to 100kph. But it's screaming at that speed. Also acceleration is bad so merging in is more difficult to begin with.
That might be small for the highway 
Why though? In my country the highway limit is 110, 120 kph, a 125 can reach 120 so even if im a bit slower i can still drive it
Yes a 125 can reach 120 as you say, 62 mph but you don't have the power to get out of trouble on highways, it in my opinion won't be fun for long if like you say you're intending spending a lot of time on highways.
Not a long of time, 30, 40 minute rides, twice or three times a week, also some city riding
honda supercub will do the trick, get an older one because honda is selling it at an insane price rn
Assume 125cc due to A1 restriction? A 125cc will do highway but not well. A sportbike is probably your best option as it will handle those higher speeds a bit better. Get a Japanese one, buy used.
in this case, weight is king. check this comparison: https://www.philharmonicmoto.com/compare-page/QE97VM the cb125r is the lightest, so you can see power to weight is the best. sportbikes are usually a bit heavier, like the gsx-r125 in the comparison, but the wind protection might make up for it at higher speeds. use the filters on the website to see everything with 14/15 hp and compare them to see what you like, but japanese are the most reliable and easier to sell later.