So, what are the alternatives?

There’s tons of similar SBC’s out there from Chinese manufacturers, like Orange Pi, Banana Pi, etc; usually using mediatek RISC-V or rockchip ARM processors. They’re all poorly supported on the software and documentation side though and take more work to get going, which has always been where Raspberry shined- nobody else has made embedded computing so easily accessible with click and go OS options and continuous kernel maintenance.
Probably the only board closest to software parity is the pine64 boards… but it’s still not quite as good.

This is the key point for alternatives. None seem to have the community and support (docs, s/w quality etc) that is remotely close to that of the Raspberry Pi.

They have more features though, like extra Ethernet, PCIe brackets and M2 slots on the board

Those features don’t mean shit if you can’t use a modern OS after a couple of years.

Why could you not run a modern OS after a couple of years? Those SBC manufacturers did not invent an entirely new processor architecture for their computers, you can just generically compile the kernel (plus maybe some slight device tree work).