So you use the same static IP on your router menu, and on RPi, right? In that case it could be a router problem, and your other network devices have the same problem.
No the static IP is reserved manually on the router DHCP Server but even if I don't do this and manually set the IP on the RPI4 using an IP outside the DHCP Server range the same thing happens i.e. rpi4 requires a reboot
If I was to reboot the router or just for a test remove the ethernet cable the RPI4 running LE12, and previous versions, the RPI4 does not refresh the network connection, whereas given the same scenario all other devices on the network do refresh their connections and are fine, I can see the other devices refresh happening within the router logs - nothing comes from RPI4 until a reboot; the RPI4 using manjaro for instance does refresh the connection