E.g. OVH, Hetzner, TransIP... idk whatever kinda server you like. Or repurpose an old laptop at home, for a few Watts you get something that's usually more powerful per ¤ than a VPSes (or "cloud instances" in newspeak). Then install a Matrix server, add your domain, and you've got your own Signal alternative.

Or just use the standard matrix.org home server if you're just trying it out / don't mind a not-super-fast home server. Or one of a dozen public Matrix servers: https://www.hello-matrix.net/public_servers.php