If you plan to keep the Fujitsu Futro S920, you could open it up, remove the atheros mini PCIe wifi module and simply replace it with another wifi 5 (802.11ac) or wifi 6 (802.11ax) capable device. While doing so, take care to choose similar form factor.
mt7915 as PCIe seems to be rare in german market.
mt7921, you could go for, if you feel adventurous. Since it is a very new device drivers have to mature still.
Found some mt7921 on german amazon:
https://www.amazon.de/s?k=pcie+802.11ax+mt7921&i=computers&rh=n%3A430173031&s=price-asc-rank&ds=v1%3AmGEP9QtnMP%2FgAOwvRf%2F4%2BJ9zxYXsjv0rO28sqOZbyM0&__mk_de_DE=ÅMÅŽÕÑ&qid=1679133267&ref=sr_st_price-asc-rank
Or here:
Keep in mind, if you want to run your device in accesspoint / repeater / bridge / monitoring mode, then best wifi 6 Linux supported cards are from Mediatek and Qualcomm. AFAIK Intel (which offers many cheap M.2 cards), only supports Linux with wifi drivers that are capable to be run as "client". Have a look at Suggestions on x86's mini pcie / m.2 wifi card: both in AC & AX for ap mode to find PCIe devices that are access point capable.