Stickstoffmangel?

Hey, What has the weather been like the last little while? While the other 2 answers are not wrong, older leaves do eventually just die, your plant is too small for this to be the cause. My guess is that you have had some heat and the leaf being close to the soil in the sun, it got a bit too warm.

The lowest oldest leaves often do this because they do not get enough light and is somewhat normal. It can also show that your plant is a little bit hungry for nitrogen during the "stretch" as you thought. Now that she is entering the bloom phase, you will have to give her mild fertiling every 7 days or so.

könnte schon auf eine bevorstehende knappheit hinweisen, wobei diese blätter mit 3 fingern auch gerne einfach mal absterben, die sind ja auch schon sehr alt und bekommen wenig licht