Foss secure e2e videocall app or site?

If you're ok with Jitsi, and you already use Brave, note that Jitsi is baked in. See https://brave.com/talk/ and check the "Who provides the Brave Talk service?" question:

The Brave Talk service is provided in partnership with 8x8. And the service is built on the open-source Jitsi platform.

(Note that 8x8 owns Jitsi)

See also the "How are my calls with Brave Talk encrypted?" question:

To start, all video and audio data transferred through Brave Talk is encrypted via transport layer encryption. This is similar to how many websites use HTTPS to ensure your traffic can’t be captured on public networks (e.g. coffee shop WiFi).

The video and audio from your call are transmitted to other participants with the help of a Video Bridge server that’s run by Brave’s partner, 8x8. When you enable Video Bridge Encryption in Security Options, your browser exchanges keys with other call participants, and these keys are used to encrypt the video and audio streams. Only people with keys can see your calls. Assuming honest but curious behavior, neither Brave nor its partner, 8x8, have this key by default.

However, there are some important limits to Video Bridge Encryption. If you want to include a phone participant in your call, have more than 20 participants, or want to include users with incompatible browsers (Safari, most iOS browsers, and browsers based on Chromium version 83 or below), this encryption setting will not work. If you record a call, 8x8’s servers will receive a set of keys to decrypt the video/audio stream in order to process and store that recording. Brave will continue to improve Brave Talk’s encryption properties and work to remove some of these limitations.

Read a more detailed description of Jitsi encryption (the open source basis for Brave Talk).

Session is crypto-currency bound with dubious twists.