hello, tell me how to summon already lit dynamite

Do

Use Summon living entity (TNT) if your want it to insta-explode

if you want it to wait then you can do something like this

Place TNT at XYZ
Wait 50 ticks then on server side:
Do:    Remove block at XYZ

          Summon living entity (TNT)    

You can also use the "Explode at" procedure if you'd want to.

If you want a tnt with some explosion delay, go to "world management" then take the block execute command or something like that, then type in: summon minecraft:tnt ~ ~ ~ {Fuse:80} I do have to mention, you need to type Fuse with a capital letter, otherwise, the game won't recognize