There are a lot of folding bikes that can compact small enough to go in an overhead bin or get checked as luggage. You could also just stick with budget non-fol

There are a lot of folding bikes that can compact small enough to go in an overhead bin or get checked as luggage. You could also just stick with budget non-folding options then sell your old one and buy a new one at your destination. You'll lose some money every time but on the upside you can buy a bike that fits your lifestyle at every destination, or skip getting one when it doesn't make sense. Brompton bikes are one of the classic recommendations for folding bikes but there tons of other options nowadays as well.