I've initially used Let's Encrypt to generate the certificate for gluonspace.com without noticing these certificates expire and therefore need renewing every three months. Therefore, due to the TOFU nature of Gemini, to avoid requiring you to trust me again every threee months, I'll be changing to a long lived self signed cert for this domain this week.
So that's it, you can expect your clients to warn you about a certificate change and therefore require you to trust the new one. This is perfectly fine and common within the Geminispace, at least until we find a way to address the shortcomings of TOFU. This is just a heads-up so that you have an extra way to confirm that the owner of this domain made the change.