Easiest solution for Windows is Voicemeeter Banana/Potato, in my opinion
Install, restart, and set windows sound
output to Voicemeeter
Input
Set Reaper to WASAPI, and set input and output to the VAIO3 Voicemeeter AUX
https://i.imgur.com/RjI1abJ.png
In Voicemeeter, go to the top right and where it says A1 click and select your L-20 ASIO driver
Under Menu > System settings/options you can configure the usual buffer size stuff if needed
But most importantly here, if you have a microphone, go to Patch ASIO to strips: and put 1 1 in the first two boxes by clicking them, as you can see in my screenshot.
https://i.imgur.com/Jt8PWlE.png
On the far left channel you should now have controls for your microphone.
Send it to B1 for the Zoom use, and A1 if you want to hear yourself.
The VAIO, AUX, and VAIO 3 channels are for outputs from Windows and select programs. All running software should appear here in one of them. Reaper should appear in the AUX channel as we set earlier.
Anything you want to send to Zoom, set to B1 output. A1 to hear it yourself.
That's it.. now in Zoom set 'Same as System' for audio in/out.
Note: Zoom will heavily compress and filter the sound. If you want really clear audio, try Discord instead. I've streamed music over Discord's algo and its as if the listener is hearing an mp3.. until someone talks then it tries to choke it as usual.