No matter what you try, however, this time, there’s no possible workarounds that could allow you to use YouTube Music on any operating system older than Wear OS 3.
Smartwatches prior to the Galaxy Watch 4 series max out at Android 9 (API level 28). A mobile security analyst, who runs by the Twitter tag of @linuxct, managed to get over this initial hurdle, after he entered and modified the application code, manually lowering the requirement to an API minimum level of 28.
This fix finally allowed @linuxct to install YouTube Music on the Moto 360, but other problems arose. When he opened the app, he found other features weren’t working properly and were breaking on him, rendering the app unusable. Lowering the API level requirement had broken the Google login support, without which the app cannot function.
Yes, I decompiled the APK and decreased the min. API version to 28, which should match current H-MR2 devices, and I was able to repack and install it. However, because of resigning the application with my own key, the app loses its connectivity to GMS and I can’t login… (1/X)
— linuxct (@linuxct) August 26, 2021
This failed group effort to get YouTube Music working on older watch OS’s unfortunately means that if you aren’t willing to upgrade to the newest Galaxy watch generation, you won’t be able to avail yourself of the popular music streaming service.
More Wear OS 3 and higher devices are going to be piling in over the following years, however, so there will be plenty of opportunities to upgrade eventually, and gain access to all the features that Wear OS 3 has to offer.