Is there a way to capture the internal audio strean directly without loss? I know there are numerous screen capturer (Mobizen etc), but I only need the audio, not my screen.
The only conceivable way I can think to achieve this would be the use of some kind of external USB DAC (digital-to-analogue converter), which involves routing the audio out through the USB C port
I've successfully done this using a cheap adapter-type "soundcard" (the 'Sabrent Aluminum USB External 3D Stereo Sound Adapter', bought on Amazon), which involved attaching it via a USB OTG cable to my phone and then connecting its headphone jack directly into its mic jack, using a male-to-male 3.5mm TRRS cable. I don't recall the software I used but it shouldn't be hard to find a good app.
I seem to recall the audio sounding decent enough but, as you stipulated without loss, digital audio will only ever sound as good as is allowed for by the processing of the digital signal by whatever DAC is used (along with the quality of the source, for example Tidal Hi-Fi streams are lossless/uncompressed flac files, whereas Spotify maxes out at MP3 320kbs), so another way which I believe is possible - I intend to try it myself at some point - would be through the use of dedicated HiFi separates. Either a DAC/amp, Audioquest's Dragonfly range and Schiit's Fulla being good starting points if you're new to this sort of thing, or separate DAC and amp components paired, such as the "Schiit Stack" - their complementary and very fairly priced Modi DAC and Magni headphone amp/pre-amp.
For this to work (without using a PC, anyway), you'd have to connect a TRRS jack cable from the amp to your phone's headphone jack, which also acts as a mic and should - as far as I'm aware - be picked up by Android audio recording apps. Of course if you own a PC that could make things a lot easier, just hook it up to your amp and record with something like Audacity.
Oh and if you go for the second, more expensive/higher fidelity option, I STRONGLY recommend the USB Audio Player Pro app. This allows you to bypass the phone's internal DAC, acting as something of an interface for/with your DAC by directly feeding it the raw audio data/signal. It's an all-round great audio player and has many great features, especially support for Tidal (the audio stream playing through it rather than having to use the service's own dedicated app) and a few other streaming services
Hope this helps.