I have just uploaded a new release of firmware for the T-Deck, which updates it to ESP uLisp Release 4.6c, including support for the T-Deck PSRAM to give a workspace of 1000000 cells.
For example, you can run the sieve benchmark which uses a 1000000-element bit array to calculate the largest 6-digit prime:
> (time (sieve 1000000))
999983
Time: 92.6 s
Get the firmware here: https://github.com/technoblogy/ulisp-tdeck
For more information: LilyGO T-Deck uLisp Machine