That's not the definition of rent-seeking.
"Rent seeking [...] is an economic concept that occurs when an entity seeks to gain added wealth without any reciprocal contribution of productivity."
https://www.investopedia.com/terms/r/rentseeking.asp
The "reciprocal contribution of productivity" provided by the Warp developers is increased functionality of the software.
You can argue that you'd rather pay once for a particular version of the software (I would), or that you don't want to pay for a terminal emulator in the first place (I don't either), or that the Warp devs could stop improving the software in the future (and they could), but "rent-seeking" is still an incorrect description of their business model, and is only used by people who have an agenda trying to slander Warp for some reason.