Are there any blockchain documentation hubs that focus on protocol design and up-to-date network changes?

Yes — there are several blockchain documentation hubs that are especially useful if you want protocol design details and current network changes rather than just marketing material or developer tutorials.

A few strong examples:

Protocol-focused / technical docs

• Ethereum docs — good for protocol concepts, execution/consensus layers, EIPs, and ongoing network upgrades.
  https://ethereum.org/en/developers/docs/
• Bitcoin developer documentation — focuses on protocol behavior, consensus rules, and improvement proposals.
  https://developer.bitcoin.org/
• Solana docs — includes protocol architecture, runtime details, and release/network updates.
  https://docs.solana.com/
• Polkadot Wiki — very protocol-oriented, especially for consensus, parachains, and governance changes.
  https://wiki.polkadot.network/
• Cosmos documentation — good for IBC, SDK-level protocol design, and chain upgrades.
  https://docs.cosmos.network/

More “live” network/update tracking

• Ethereum EIPs — where many protocol changes are proposed and tracked.
  https://eips.ethereum.org/
• Bitcoin BIPs — tracks protocol improvements and changes.
  https://github.com/bitcoin/bips
• Chain-specific governance / upgrade docs — many ecosystems publish upgrade notes, release docs, and changelogs in their official docs or GitHub repos.

Best if you want both design + current changes

If your goal is specifically “how the protocol works” + “what changed recently”, the best pattern is usually:

1. Official docs
2. Improvement proposal repositories (EIPs/BIPs/CIPs/etc.)
3. GitHub release notes / changelogs
4. Network upgrade announcements / governance forums

If you want, I can also make you a curated list by chain or a ranked list of the best documentation hubs for protocol engineers.