For those of you seeking short-term (1-3 month) ultraliquid USD parking facility in IB, I found several US 1-3 month Treasury bill ETFs like BIL and SGOV.
Assume you adjust SMART routing to VLow (High volume exchange with lowest fee), you can get your trades executed with as low as 0.24 USD instead of the usual "0.35 USD". BIL is liquid but expense ratio is high at 0.14% p.a., SGOV's expense ratio is low but that is due to temporary fee rebate by BLK which would terminate on 30th June 2023 (after which it would be around 0.14-0.15% p.a., on par with BIL). Moreover, SGOV has about 6% asset exposure in its own institutional cash fund which has Treasury floating rate notes and introduces additional counterparty risks with banks like Citi, Credit Agricole etc. So, not truely "risk-free".
I did some IRR calculations and found that you can get returns of about 1.3% p.a. for the 2-month holding period, factoring 30% WHT for the monthly distributions and 0.24-0.35 USD commissions, charged twice (once during purchase, once during sell).
Much lower than contemporary 2-month UST yield, but better than holding everything on cash balance and let IB suck all your interests away I guess. After all, in terms of opportunity costs, there is nothing more "risk-free" than risk-free rates. So, in theory, as long as better than 0% p.a., one should bite.

DBS 1mth FD gives 3.42%, 3mth 4.28%. If you have >10k, IBKR giving 3.33%. Wouldn't this better than buying ETFs that gives 1.3% but may subject to various risks?