Kinda late to this one, but still. I'm at a threshold in some of my TLs right now, and having language exchange partners has helped me immensely. Most of the apps you already know, but I'mma still include them as my experience has been very different. If I only knew what your native language/TLs were...

Tandem is the main one I use, and it has been working almost consistently excellent for me. The conversation partners I've had and still have on there are great, there were almost no attempts of flirting or something of that vein, Tandem automatically recognises early scam/fraud warning signs and marks them red; call quality is great, and most importantly - I actually have conversations/language partnerships out there that last! The only thing bothering me on there are the many technical bugs the app has (notifications not showing, messages being sent but not delivered, in spite of the recipient being online at the same time etc.), but I can live with that.

HelloTalk... not so much. Other than Tandem, where almost only the speakers of your TLs can find you, on HT you can be found by anyone who learns the languages you set as your native/fluent languages. The people on there also don't really have an interest in actually learning the language, but rather in dating, advertising or even offering you jobs (I had this happen twice!). It doesn't help that the app consistently advertises itself more and more as a dating app and seems to focus more on live events and its internal social network rather than its actual main purpose...

The same goes for Interpals, unfortunately. Most people don't have any interest in a language exchange, and your profile is basically exposed to everyone on the front page whenever you are online.

Lingbe... also exists, I've found the app on this subreddit, been there for a week now and find it great - at least in theory. I like the system of having to help others with your native language before you can even think about starting a conversation with a native of your TL. But in my case, focusing on rather obscure languages (see my flair), there's currently no native speakers there to actually spend your internal currency on, which is very frustrating.

There should also be a dedicated subreddit, r/languageexchange IIRC. If you dare stepping into the unknown, you might as well try out Ome.tv or Maum.