20k tabs? I struggle to see how someone could go through that many tabs, even over a long period of time. Your workflow is something the browser was never made to handle.
Try some popular non-Mozilla tab suspend extensions. I doubt that they all operate the same way.
Check out Termux’s GitHub. I would link the issue but not sure if linking is allowed. You’ll find that the Play Store build is currently broken, but the F-Droid (alternative FOSS software store) build works fine.