New feature added to auto-split big UTXOs at your preference.
If you add splitutxo=reward or splitutxo=any to your tha.conf, feature will split big utxos to as many smaller ones yet still eligible for staking. It's one split transaction per block to avoid mempool spam, efficient enough because of multiple outputs. The difference between reward and any is the first picks only from your block rewards, second picks any among rewards and received coins. Still, there is a limit for splitting candidates, to be <= 100 THA in order to keep number of generated outputs under 1000.
Qt gui wallet has a "live" control of splitutxo feature, which can override tha.conf settings. It's placed in the main menu.