For most people at home their router also does firewalling and NAT, and that is enough.
It is important to note (as was pointed out by others in this thread) that one must also consider threats emanating from within the LAN, as well: Do you have guests that you allow onto your network with potentially un-vetted devices? Do you have other network-capable devices connected to your network that you cannot guarantee their security? Can you guarantee that there are no unintended services with potential security vulnerabilities listening to ports on your device? If so, it is worth considering, at the very least, a packet filtering firewall, e.g. nftables, and if you cant trust the services running on your device, perhaps also an application layer firewall like OpenSnitch.