Yellow leaves / droopy ?

Stems purple, oxygen deprivation, in the xylem channels. Limited oxygen I rootzones or too high rh in atmosphere for too long..The root zone becomes oversaturated depleting oxygen. Soon as oxygen gets low iron cannot be converted and becomes unavailable. With no iron the chloryphyll cannot replenish causing lime green all over. But it does look like magnesium def is creeping in the bottom also. Tips look to be around 1.5ms/cm from my experience getting close to salt ion capacity in the medium also.

Magnesium deficiency.

It doesn’t look like a nutrient burn at all, rather overwatering. I think you solved this problem yourself without overthinking it.

zu viel Wasser😰

fully saturating a medium does not cause root rot. that's what you should do each time... if not waiting long enough between irrigations, that could cause root rot. One time will not cause it. There is more than one cause of interveinal chlorosis, so you may need to let it progress a bit more to confidently diagnose. If it is Mg related, should see some spots coinciding with the chlorosis, which i don't see here. Chlorosis at bottom (mobile) is a bit weird, but i guess it could be Fe deficiency -- this would be unusual.. trace element issues are usually a side effect of pH issues or nute-lockout. it's uncommon there's an actual, physical trace element deficiency, but not impossible. if you've been engaging in bad irrigation habits, that can definitely be a cause of various symptoms. 1) fully saturate - if in soilles, also religiously get 10% runoff or more -- never let it sit in its piss, either way. 2) wait for appropriate dryback and repeat. while there is a little leeway in exactly how much you allow it to dryback between, these basic steps are the correct way to irrigate. if doing it wrong, fix it. you do not whimsically choose the volume of water to provide... you give what it takes to accomplish the first step and no less. if you allow the same dryback (loss of weight) then you can roughly predict the volume needed for the sake of any fertilizer mixing.

Overwatering / Root Oxygen Deficiency Leaves may turn yellow because roots aren’t getting enough oxygen. Allow the medium to dry slightly between waterings the pot should feel lighter before the next irrigation.

it could be anything u want 👆 but not something that u've thought about 😅