Most people I know have actually moved toward the streaming services themselves if they have the built-in watch party features. Hulu has a feature that lets you sync up with friends and chat in real-time, and some shows on other platforms have similar options baked right in. It's not always advertised heavily, so it's worth checking the app settings or looking for a "watch together" button when you start an episode. The advantage is everyone's already in the same place where the show is playing, so there's no juggling multiple tabs or apps.
If the show you want to watch doesn't have that option, Reddit communities are honestly still the go-to for a lot of people. Subreddits dedicated to specific shows often have live discussion threads when episodes air, and you get a real-time chat with folks who are genuinely invested in what you're watching. It's less private than a dedicated watch party with just friends, but the energy can be fun. There are also some smaller platforms like Teleparty (formerly Netflix Party) that still work for syncing playback, though honestly some people find them clunky now compared to native features.
For catching shows with a specific friend group, you might also just ask the network or streaming service directly in their support - sometimes they have recommendations or workarounds specific to what you're trying to watch. A lot of shows that air live on cable or streaming have companion apps or official Discord servers run by the networks themselves, which might actually be worth exploring even if you're avoiding general Discord for other reasons.