No, you should not assert the transceiver tx_pma_elecidle signal indefinitely on Intel® Stratix® 10 L-Tile or H-Tile devices.
The tx_pma_elecidle signal is similar to an analog reset signal. Asserting analog reset signals indefinitely can degrade transceiver performance. You can read about this degradation in the “Unused Transceiver Channels” chapter of the Intel Stratix 10 L- and H-Tile Transceiver PHY User Guide.
This information will be added to a future version of the Intel® Stratix® 10 L- and H-Tile Transceiver PHY User Guide.