Yes, the 10GB LAN port can be used as a normal port to the router, for example. It is a 10 GbE RJ45/SFP+ combination uplink port that also functions as a regular 10 Gigabit Ethernet port and can transmit data at up to 10 Gbit/s. The prerequisite is that the appropriate power supply unit (e.g. the original Ubiquiti AC power supply unit) is available to supply the switch with power.

Short-term solution: A third-party 54 V / 3 A power supply unit (5.5 mm) can operate the switch with sufficient PoE power.

Found the solution, maybe it will help someone else: In the DHCP Options -> Set option 43, enter the value as a string and the IP of the controller in Hex.

The switch can be operated with a PoE++ injector, as it can be operated with PoE+++ or an AC mains adapter. If you use a PoE++ injector, the output power of the switch will be limited, as the PoE++ injector delivers less power than a PoE+++ injector or the official mains adapter.

The device generates moderate heat, comparable to similar PoE switches. It can function in a small power box without active ventilation as long as sufficient passive air exchange is possible. However, ambient temperatures permanently above 40 °C should be avoided.

The Ubiquiti USW-Flex-2.5G-8-PoE switch is supplied without a power supply unit as standard. It can be operated either via PoE+++ (Power over Ethernet) or with a separately available 210 W AC power supply unit. You can find the matching adapter here: https://www.galaxus.ch/de/s1/product/ubiquiti-ac-adapter-210w-netzteil-netzwerk-zubehoer-54373140.