Where to keep an emergency fund?

I want to save ~3 months worth of income to ensure myself in scenarios where I need to have money available, but the market is down.

On the other hand, I dislike the idea of inflation eating away at this sum, unless that is my only reasonable option.

I use Scalable Capital, and set up a monthly savings plan that buys the "Xtrackers II EUR Overnight Rate Swap (Acc)" ETF on a monthly basis. My reasoning was that this ETF was (1) stable in price, so I won't find myself in a situation where I incur losses because I need to sell stocks in a bear market, and (2) still growing stably at around 3.9% per year, meaning that I am not losing as much money as I would be if I were simply keeping it in a bank.

One of my most important considerations is that I want to deal as little as possible with the German tax system, which is why I chose Scalable Capital, who do that for me.

I am a German tax resident at the moment, and a tax resident of my home EU country, where I will move back within ~3-5 years. Is my reasoning correct? Or am I missing something important, like a different kind of German tax calculation for this ETF, which would make it a more or less stupid investment in my case?

Are there any alternatives? I do not know how to invest directly into an MMF on Scalable Capital, or which one to pick, or how they differ from ETFs (I don't even know if you have "shares" of an MMF, for example).