Where to “Park” my cash reserves?

Hey everyone, working on changing up my investment portfolio a bit. I currently have a 10% (~$20,000) allocation in cash reserves. I use TDA/TOS as a brokerage. Cash to me, just means holding the money on the brokerage and letting it sit there until a “buying opportunity” arrives.

This cash is only there for significant, almost, generational, buying opportunities. ie: Covid Crash, Dot Com bubble, 2022 great reset.., 08', etc.

Anyway, are there any recommendations on a low beta, liquid, alternative to gain interest on this cash? I'd prefer to keep everything on TDA, and I'm currently getting a  .01% return from holding cash through them. I'm assuming there has to be a decent ETF out there?

Thanks