Due to small-yet-persistent demand in .NET Compact Framework 3.5, we will continue to provide and maintain .NET CF 3.5 binaries after 2021-04-13 until at least 2022-04-13 as long as your support contract is still active. However, these binaries will no longer be covered by our standard support terms (contact email@example.com to discuss custom support arrangements for end-of-life platforms).
Next year, we plan to add TLS 1.3 support to Rebex HTTPS for .NET Compact Framework 3.9, where our experimental build appears to work without any issues. Unfortunately, the same cannot be said for the .NET CF 3.5 edition, which seems to be pushing a lot of legacy devices over their limits. We plan to publish a new experimental build soon to see how much interest in this there is and how well it works.
However, I am not sure whether our managed Chacha20/Poly1305 implementation would be faster than our AES/GCM on .NET CF, because the AES part is aided by CryptoAPI's native implementation.