TL;DR
After BIP-925, the inactive Timeless VeBalGrant still has approximately 10,286.807445 USDC in unclaimed FeeDistributor rewards. These were not recovered by BIP-925 because withdrawBalances() only handles BAL and WETH.
The DAO multisig can recover the USDC by atomically calling claimFees(FeeDistributor, USDC, DAO, 0) four times. This is necessary because the grant has accumulated more than 60 weeks of unclaimed USDC, while the FeeDistributor settles at most 20 weeks per call.
Technical Specifications
There is a PR with the DAO Safe payload and successful simulations available at BIP-XXX: Claim Timeless VeBalGrant USDC fees by mendesfabio · Pull Request #2882 · balancer/multisig-ops · GitHub