Which Linux based firewall would you recommend

Sorry, missed this topic. The answer is it depends on your distribution. Most will have a firewall of some type. For the longest time, most used "iptables", but "firewalld" seems to have replaced that in many, especially the ones that were mirroring what Red Hat was doing. These are mainly just for basic security (it is very possible to use them for some very complex behavior, but the out of the box behavior depends on the distribution).

The actual "firewall rules" are in the Linux kernel. The kernel has had "netfilter" a long time. The "iptables" was a low level tool to interact with the netfilter. (Before iptables there was "ipchains".) Since 3.13 the kernel has had also "nf_tables" that supercedes-or-something the netfilter. The low level tool is "nft" (and there is version of "iptables" that is wrapper/translator to nft).

The low level is not very "humane", so many distros have a "front-end" that talks to kernel directly or with the low level tools. Examples are FirewallD and UFW. They present the user more "logical" config that they translate to kernel rules. Some distros (e.g. embedded in home routers) may have just (browser-based) GUI interface, where they offer rather minimal set of logical options.

As said, the default ruleset depends on the distro. The "own needs" do most likely need some action (unless you are more "typical" than you expect).