I was under the impression that newer kernels had much better power management integrated within and that it made things like TLP unnecessary. Is this true? Should I be using it?
I noticed that Ubuntu 21.04 has power schemes available there very similar to Windows. Do these do what TLP does, or will see even better gains using it in addition to these schemes?
TPM is the Trusted Platform Module. It handles cryptographic functions. Most common and visible thing it does is handle Bitlocker or LUKS decryption keys (for full disk encryption) but it does a lot more than just that. The OS is able to handle certain crypto functions off to the TPM which is a discrete chip on the motherboard and runs outside of the OS. This makes it much more secure than using purely software to encrypt/decrypt things. It is now a requirement for Windows 11 and has been a standard on motherboards for a few years now.
Sorry auto correct made an error. I fixed it. I know what a TPM is, and it has nothing to do with what I’m talking about here. (or what I intended to talk about) 
So IME: TLP has a huge impact on battery life by adjusting key tunables to enable power management, set power profiles, etc. In something like Windows these functions are built until the OS power management subsystem. On Linux, these userspace tools (of which there are a few) fill the same role.
Now, in Ubuntu, as you’ve indicated, they’ve incorporated power-profiles-daemon, which is another alternative to TLP. It’s entirely possible it does all the right things out-of-the-box! If someone were to run some experiments and report back, that’d be… pretty interesting… 