Try setting the port to 80

Are you connecting by domain name or by IP address?

So a quick search resulted in this issue from the Yattee repo:

https://github.com/yattee/yattee/issues/354#:~:text=Invidious HTTPS Instance needs to be configured with,links in the external API used by Yattee.

And the highlighted answer states:

Invidious HTTPS Instance needs to be configured with this settings:

external_port: 443 domain: whatever.it.is

Without it, the Invidious frontend will show thumbnails fine but will produce wrong links in the external API used by Yattee.

I just spun up an Invidious instance a week or two ago and I have the same issue using the Yattee app on iOS. If I find an answer I’ll post the solution.