i can’t send dm to people other than me

You issue is with the ID you placed it as a string instead it should be victim.id. Also you didn’t use the message variable

Use it like this {prefix} dm @user Hello this is a test

@bot.command()
async def dm(ctx, victim: discord.Member, *, message: str = None):
    if message:
        await victim.send(message)
    else:
        await victim.send("No message context")