From what I understand, there isn’t really a right or wrong way, just whatever works for you. If you lock your knees too early then it ight be harder to get your hips through, if you wait too long to lock your knees then you might not be able to lock them fully and you can get called for soft knees. It seems like most good sumo deadlifters lock their knees before fully extending their hips, but there are some who lock both simultaneously as well. I remember Mark Robb discussing this on the RTS forum a couple years ago, he was having some lockout issues due to when he locked his knees. He has a few IPF masters world records and pulls over 700, in case you don’t know who he is.
Anyway, with lighter weights that you can pull for 5’s and 8’s it probably won’t make a difference. You would have to pull something at 85-90% or more and even then you might be fine with whatever feels natural at the moment until you get significantly stronger, and you can always make adjustments as necessary. I’m not a great deadlifter, but I seem to automatically lock my knees when my hips are about 3/4 of the way locked out and I have no problem with that.
The only possible cause for concern that I see here is that you lean back a lot at lockout, that can force your knees forward and cause them to unlock. Bryce Krawczyk said in a video that he had issues with that when he first switched to sumo and @Vincepac1500 missed a big pull in a meet because of that, although I believe he said he had some issues with balance as well. Just aim to stand fully erect (no erectile difficulties) and don’t get in the habit of leaning back or shifting your weight back unless you really feel like the weight is going to make you fall forward.