How to structure my savings?

Every month I put a % of my paycheck as an investment into VUAA on Scalable Capital. Another % of it is going into a "savings" pile, which I think of as my emergency fund and/or buffer.

I am using Commerzbank's Topzinskonto to hold this savings fund at the moment, which has a promotional APR for the first 6 months. These 6 months are expiring soon, and I need to look for a new place to park this money.

It seems like most of these "high-yield" savings accounts in German banks are also have promotional APR actually, and you lose the yields after the first 6 months.

What are my best options? Currently, I plan to keep like 1/2 of the "savings" pile parked in a MMF ETF so I get a "true" 4% yield without having to think about it further. However, I see two drawbacks:

  1. Some kind of institutional risk. I am not super well-informed here, but I do know I am no longer holding cash in a bank if I buy an MMF ETF, which means it is probably more risky thank a savings account in a bank.

  2. Money isn't available instantly. Sometimes, I go over-budget, and an advantage of the Topzinskonto is that I can take a bit of my "buffer" to cover this expense and then put it back in once my next paycheck arrives.

At the moment I think I am okay with swallowing both of these drawbacks (taking the risk, and saving slightly less so I don't need to ever take out of my buffer).

However, I am wondering if someone has some useful insight into what to do in my situation. Maybe I am severely underestimating the risks involved in MMF ETFs, and they should never be used in place of a savings account? I lack the context here.

Other factors:

  • Employed in Germany