But with an external USB 3.1 Gen2 SSD it looks much better. Rate 450 to 500 mb/s.
Had tried to first an Intenso SSD. But was already broken as a new SSD a sector and it could not install the OS.

With the Emtec SSD 128GB X210 (ECSSD128GX210) it ran immediately and runs now already over a year.

But important:

Be sure to order a good shielded USB C to USB A cable. The supplied USB cable is so bad that the wifi no longer works.