Sit them down like an adult and tell them that wasting 20-30 mins of 5 of your closest friends time every week isn't a good quality.

Tell them their own seperate start time 30 minutes before the others?

My grandmother would tell each of her grown adult children a different time to show up in order to get everyone there on time.

Give their character a disease where they take damage every 10 minutes the player is absent without notice

Funny story: because I was always late, my old group started giving me earlier times to show up. Because these times aligned better with my trains and subways, I started showing up on time. Except they'd lied to me going my being late would actually make me arrive at the same time as everyone else. But now I was half an hour early and they were unprepared.

Only tell that player that the game starts at 6pm instead of 7pm, everyone else tell that it starts at 7pm. If they are half an hour "late" they will finally be the one waiting for the others to finally show up.

Give out all the best loot in the first 20 minutes. You beat a boss at the end of a session? "Alright, we'll go over the loot beginning of next session"

Give them an earlier time. If they find out that they're given an earlier time and get salty about it, they have bigger problems.

Make their PC cursed with a broken Blink spell. They random pop into and out of existence. DC 12 for staying in this plane.

Just start the game on time without them? They can hop in when they arrive.

You can't stop me being late, I run the game. I have an entire channel in the group chat solely dedicated to my excuses for being late. They always suck. I've turned up on time to maybe half a dozen sessions in the last 6 years. If I turn up within 20 minutes of the starting time my players don't even count it as late anymore.