In the end I did it without further information, since I had enough reports that it would be possible to get through.
For the benefit of anyone else doing this route soon, here's some information.
Coming from Cali/Popayan side (north) there was a long queue of trucks, at least 50 maybe 70 or more. But it was no problem to cycle past them.
I thought the official diversion would be clearly signposted but if it was I did not see the signs. So I must have missed the turn and ended-up going all the way to the actual site of the landslide. If you also do that there are three options:
1. Try to get your bike down into the valley and up the other side on your own. I doubt you will succeed with a loaded bike because the slopes are very steep. (This guy tried that and then opted for option 2:
https://roamingtofreedom.org/2023/02/)
2. Get help to take the bike down and up. I was offered this for 50,000COP which was extortionate. (They also wanted to take the bike and have me walk separately, which would have meant they were out of sight for a while...)
3. Use the pulley system that's been rigged up for heavy baggage and motorbikes. (See picture below) That's the option I chose, paid 30,000COP but I suspect locals are paying a bit less. You then walk while your bike flies over your head!
Based on what I heard from others who had taken buses, etc, I still think it may be better to find and use the official diversion. But unfortunately having missed that I can't provide any more information about it.
