That is the way modern decent switches are working.
It is more or less part of a technical design aspect called "non-blocking switching", "non-blocking throughput" or in general non-blocking architecture. This means the switch's backplane can support each of its port at full duplex speed.
For example, if a switch has twelve 10GbE ports, the switch's backplane will support at least 240Gbit/s of switching capacity.
If you want to get started into the 10GbE world and don't want to spend big numbers on your first switch in this class, I recommend the Netgear XS712Tv2.
It is around 1000$-1100$ which is a really good deal for twelve port 10GbE BASE-T switch (with the benefit of two of this ports being dual personality ports which can either be used as RJ45 or SFP+, in case you have to connect some fiber optical gear in the future).
It is web managed, so you don't have to learn any CLI commands, which should be completely sufficient for what you want to achieve with your setup.
Little OT: I would suggest you implement some kind of firewall between your network and the network of your friend to prevent unmonitored/unwanted access between those two networks. In case some ransomware or anything alike breaks out in the network of your friend, it could spread via Windows File Sharing (SMB) or other protocols, and vice versa if any computer on your network gets infected. But as I stated, that's another topic.
Greetings,
Flo
