Seems like Piped and Invidious are both on their last legs. Public instances on both services are pretty iffy, they go down fairly often now. Freetube works well on desktop but no real way to sync subscriptions and watch history to a phone. Self-hosting Piped/Invidious might be the solution but I don’t know if it’s worth the upkeep when YouTube is actively fighting against it.
Instead of wasting your time in this conversation you might have tried just clicking on the link to see what it was. It’s simply a service where you search the platforms for a user and it spits out the RSS feed either as provided by the platform itself - Youtube - or by some libre mirror.