[USG Flex 500H + NWA130BE] - Different speedtest value between LAN and Wifi

Hi @Maverick87 I hope that what I'm writing would be considered as a pursuit to the best possible analysis, not some tech banter.

Obviously, there is always an adapter with own driver (USB-A/USB-C/Thunderbolt/PCI-Express), it's always an adapter internal or external to the PC. Also, there is always a driver that "translate" the information into human-readable. So can be normal.

Yes and no.

Data is put into subsequent "envelopes", and any "envelope" can change the theoretical maximal speed achieved. In these times, PCIe is the best "envelope" available to consumer devices, but still is not always the powerful enough-one for deliver full duplex 2.5GBe, even if PCIE 3.0x is usually "enough". It's not guarantee that any connection between adapters is delivering "enough" bandwidth to max-out 2.5GBe, expecially if it's connected throught other interfaces like USB or Thunderbolt, but it do not ends here.
USB and Thunderbolt slow down PCIe, so if the ethernet chip is more "CPU dependant" than other, the overhead for transferring such data could be also increased; Realtek are nice network adapter, delivers stable and reliable connection, usually at good performances but… there are better chips, with more computational power and that requires less CPU "attention" to work properly.

Gigabit Ethernet is quite stale network interface, roughly 1999. However, I was able to seen maxed-out the performance of these interface (via SMB) only through a "heavily" cached NAS on one side and a SATA SSD on the other one.

Therefore.
Before taking measures with speedtesters, Iperf on the same network segment is far more useful to understand what you're achieving from your network adapter. It's harder obviously compare wireless lan with LAN because also the AP plays a major role into data exchange.
Last but not least, i'm a "wire guy", whenever I cannot live without Wireless lan. It's simply better, becaue have less latency, less throughtput issues and it's connected to the switch, which can usually handly way more datatransfer than a bajillion of APs.