As long as you're doing your own whole disk encryption, you have a valid path to still be secure. However, if you're running an unencrypted disk, you're much more likely to lose your data to a non-state actor.

Well this isn't directly related to those, so maybe some derision is warranted.

Both are completely unrelated to the discussion. TPM sometimes have issues regarding their security, but you can certainly use Secure Boot with your own signing keys to ensure the kernel you run is one you installed, which improves security. And you can use TPM to either keep your FDE keys, or only part of them combined with a PIN if you don't fully trust them to be secure, so you keep strong encryption but with a bit of convenience.

Without a (properly configured) Secure Boot startup, anyone could just put a malware between the actual boot and your first kernel. If the first thing that happens when you boot is something asking for a password to be able to decrypt your storage, then an attacker can just put something here, grab your password, and let you proceed while storing in a a place it can be retrieved.

Is this scenario a concern for most people? That's unlikely. But every computer sold these last five years (at least!) can be setup to reduce this risk, so why not take advantage of it.