In version 24w33a, the explosion_power nbt was added to tnt and tnt_minecart. For regular tnts, this works fine, but for minecarts it doesn't seem to have any effect.

/summon tnt_minecart ~ ~ ~ {explosion_power:0,TNTFuse:20}
/summon tnt_minecart ~ ~ ~ {explosion_power:20,TNTFuse:20}
/summon tnt_minecart ~ ~ ~ {explosion_power:100,TNTFuse:20} 

Try the above three commands, and you will see that the three explosions are similar in size.