I'm not sure what is the difference regarding formulation ingredients. It probably has more friction modifiers like molybdenum which will be good for the gears, but not for a wet clutch.
However, the main difference is that JASO MA/MA2 is for wet clutch applications and JASO MB is for gears only (CVT) and not wet clutch. But most likely you'll be fine with JASO MA/MA2 as well.
For example, this motorcycle gear oil, regardless that is synthetic blend, is not JASO rated, however it's API GL-4 and is for wet clutch too. It also might be a good and also a cheaper option. It's very popular among scooter and 2-stroke riders that have separate engine and gear oils. So, this oil is for the grears only, not the engine
However, it will be a bit thicker than 10W-30.
https://www.motul.com/el-GR/products/74300?id=74300&product=MOTUL+TRANSOIL+EXPERT+10W-40
Product Data Sheet
https://azupim01.motul.com/media/motulData/DO/base/TRANSOIL_EXPERT_10W-40_en_FR_motul_20210426.pdf
Another JASO MB oil but is 10W-40 synthetic blend:
https://www.motul.com/el-GR/products/57701?id=57701&product=SCOOTER+EXPERT+4T+MB+10W-40
PDS
https://azupim01.motul.com/media/motulData/DO/base/motul_scooter_expert_4t_mb_10w-40_en_fr_motul_57701_20241211.pdf