Most people programmed the IBM 1620 like in the rzzzwilson comment here: FORTRAN on punch cards, running out of reach in a closed machine room. But the 1620 did have a console terminal so it could be used interactively.
Somebody at IBM built an interactive APL interpreter that ran on the 1620, but it seems this was never released:
Experimental personalized array translator system
<a href="https://dl.acm.org/doi/10.1145/364520.364573" rel="nofollow">https://dl.acm.org/doi/10.1145/364520.364573
jonjacky · · focus · HN ↗
Somebody at IBM built an interactive APL interpreter that ran on the 1620, but it seems this was never released:
Experimental personalized array translator system <a href="https://dl.acm.org/doi/10.1145/364520.364573" rel="nofollow">https://dl.acm.org/doi/10.1145/364520.364573