Is Synapse not infamous for its memory consumption and losing sync with other homeserver(s)?
The following give some details:
* https://matrix.org/blog/2020/11/03/how-we-fixed-synapses-sca...
* https://twitter.com/matrixdotorg/status/1434912387933560837
What's more the Synapse team recently announced support for Rust meaning that various performance critical sub-components can be ported over from Python.
* https://matrix.org/blog/2022/09/09/this-week-in-matrix-2022-...
As mentioned elsewhere Dendrite (Go) and Conduit (Rust) are both entirely useable albeit beta implementations.
However, I've got my own box colo'd, so I can give plenty of resources to the VM it runs in, and it seems to hold up just fine in operation.
Realistically, the bulk of my traffic is to other users on the same homeserver, so I'm less likely to notice sync/federation issues. A few people do talk across different servers, though, and would bug me if something was broken. It seems to be fine, just very CPU and RAM heavy for what a chat server ought to be using in my view of things.
I won't claim it's perfect, but it does provide for a robust and modern-ish chat service that's not reliant on the good will and data monetization of major tech companies.
And then there is Conduit which is written in Rust