Ultimately, it’s going to be down to your risk profile. What do you have on your machine which would wouldn’t want to lose or have released publicly? For many folks, we have things like pictures and personal documents which we would be rather upset about if they ended up ransomed. And sadly, ransomware exists for Linux. Lockbit, for example is known to have a Linux variant. And this is something which does not require root access to do damage. Most of the stuff you care about as a user exists in user space and is therefore susceptible to malware running in a user context.
The upshot is that due care can prevent a lot of malware. Don’t download pirated software, don’t run random scripts/binaries you find on the internet, watch for scam sites trying to convince you to paste random bash commands into the console (Clickfix is after Linux now). But, people make mistakes and it’s entirely possible you’ll make one and get nailed. If you feel the need to pull stuff down from the internet regularly, you might want to have something running as a last line of defense.
That said, ClamAV is probably sufficient. It has a real-time scanning daemon and you can run regular, scheduled scans. For most home users, that’s enough. It won’t catch anything truly novel, but most people don’t get hit by the truly novel stuff. It’s more likely you’ll be browsing for porn/pirated movies and either get served a Clickfix/Fake AV page or you’ll get tricked into running a binary you thought was a movie. Most of these will be known attacks and should be caught by A/V. Of course, nothing is perfect. So, have good backups as well.
It’s going to depend on what types of data you are looking to protect, how you have your wifi configured, what type of sites you are accessing and whom you are willing to trust.
To start with, if you are accessing unencypted websites (HTTP) at least part of the communications will be in the clear and open to inspection. You can mitigate this somewhat with a VPN. However, this means that you need to implicitly trust the VPN provider with a lot of data. Your communications to the VPN provider would be encrypted, though anyone observing your connection (e.g. your ISP) would be able to see that you are communicating with that VPN provider. And any communications from the VPN provider to/from the unencrypted website would also be in the clear and could be read by someone sniffing the VPN exit node’s traffic (e.g. the ISP used by the VPN exit node) Lastly, the VPN provider would have a very clear view of the traffic and be able to associate it with you.
For encrypted websites (HTTPS), the data portion of the communications will usually be well encrypted and safe from spying (more on this in a sec). However, it may be possible for someone (e.g. your ISP) to snoop on what domains you are visiting. There are two common ways to do this. The first is via DNS requests. Any time you visit a website, your browser will need to translate the domain name to an IP address. This is what DNS does and it is not encrypted by default. Also, unless you have taken steps to avoid it, it likely your ISP is providing DNS for you. This means that they can just log all your requests, giving them a good view of the domains you are visiting. You can use something like DNS Over Https (DOH), which does encrypt DNS requests and goes to specific servers; but, this usually requires extra setup and will work regardless of using your local WiFi or a 5g/4g network. The second way to track HTTPS connections is via a process called Server Name Identification (SNI). In short, when you first connect to a web server your browser needs to tell that server which domain it wants to connect to, so that the server can send back the correct TLS certificate. This is all unencrypted and anyone inbetween (e.g. your ISP) can simply read that SNI request to know what domains you are connecting to. There are mitigations for this, specifically Encrypted Server Name Identification (ESNI), but that requires the web server to implement it, and it’s not widely used. This is also where a VPN can be useful, as the SNI request is encrypted between your system and the VPN exit node. Though again, it puts a lot of trust in the VPN provider and the VPN provider’s ISP could still see the SNI request as it leaves the VPN network. Though, associating it with you specifically might be hard.
As for the encrypted data of an HTTPS connection, it is generally safe. So, someone might know you are visiting
lemmy.ml, but they wouldn’t be able to see what communities you are reading or what you are posting. That is, unless either your device or the server are compromised. This is why mobile device malware is a common attack vector for the State level threat actors. If they have malware on your device, then all the encryption in the world ain’t helping you. There are also some attacks around forcing your browser to use weaker encryption or even the attacker compromising the server’s certificate. Though these are likely in the realm of targeted attacks and unlikely to be used on a mass scale.So ya, not exactly an ELI5 answer, as there isn’t a simple answer. To try and simplify, if you are visiting encrypted websites (HTTPS) and you don’t mind your mobile carrier knowing what domains you are visiting, and your device isn’t compromised, then mobile data is fine. If you would prefer your home ISP being the one tracking you, then use your home wifi. If you don’t like either of them tracking you, then you’ll need to pick a VPN provider you feel comfortable with knowing what sites you are visiting and use their software on your device. And if your device is compromised, well you’re fucked anyway and it doesn’t matter what network you are using.