tl;dr: my PHEV does change gears when in EV mode, as weird as it sounds
So, I drive a Hyundai Ioniq Plug-in Hybrid EV (PHEV). It’s a hybrid with a larger battery so you can plug it in and drive fully-EV on the battery for about 30 miles/50 kilometers or so. The freaky thing is that the EV motor is connected to the transmission, so it does switch gears sometimes and you can feel it when it does. Even freakier is that this also applies to regenerative braking: when you slow down from a high speed, you can sometimes feel it switching gears while you brake. That all isn’t too bad since it’s got a dual-clutch transmission and so it switches gears pretty quickly, but it can still be a bit freaky at times.
Additionally: there are some people who have converted antique cars to EVs, but to save money they didn’t touch the transmission and instead elected only to replace the engine. They still have manual transmissions in them, though I suppose you could probably just find a suitable gear to leave them on 100% of them time. Still, you can, in principle, switch gears on them.
Typically I’ve seen people keep their car in 2nd (or reverse IIRC? That way your controller doesn’t have to support reverse and you don’t have to put in a new switch on the dash) in electric swaps. Also you don’t use the clutch pedal to start, only to change gears, which is a bit freaky when you’re not used to it.
On the highway there might be value in switching to a higher gear though, torque/efficiency curves aren’t perfectly flat even on electric motors. I would be curious to know what gains would be had on a modern electric platform like an ID.3 if one was to put in a cheap two or three gears sequential/manual transmission (for all I know the efficiency gains would not offset the additional losses from the clutch and gearbox, and even if they are some gains I’m sure that they do not make up for the inconvenience/lack of comfort of a MT).
tl;dr: my PHEV does change gears when in EV mode, as weird as it sounds
So, I drive a Hyundai Ioniq Plug-in Hybrid EV (PHEV). It’s a hybrid with a larger battery so you can plug it in and drive fully-EV on the battery for about 30 miles/50 kilometers or so. The freaky thing is that the EV motor is connected to the transmission, so it does switch gears sometimes and you can feel it when it does. Even freakier is that this also applies to regenerative braking: when you slow down from a high speed, you can sometimes feel it switching gears while you brake. That all isn’t too bad since it’s got a dual-clutch transmission and so it switches gears pretty quickly, but it can still be a bit freaky at times.
Additionally: there are some people who have converted antique cars to EVs, but to save money they didn’t touch the transmission and instead elected only to replace the engine. They still have manual transmissions in them, though I suppose you could probably just find a suitable gear to leave them on 100% of them time. Still, you can, in principle, switch gears on them.
Typically I’ve seen people keep their car in 2nd (or reverse IIRC? That way your controller doesn’t have to support reverse and you don’t have to put in a new switch on the dash) in electric swaps. Also you don’t use the clutch pedal to start, only to change gears, which is a bit freaky when you’re not used to it.
On the highway there might be value in switching to a higher gear though, torque/efficiency curves aren’t perfectly flat even on electric motors. I would be curious to know what gains would be had on a modern electric platform like an ID.3 if one was to put in a cheap two or three gears sequential/manual transmission (for all I know the efficiency gains would not offset the additional losses from the clutch and gearbox, and even if they are some gains I’m sure that they do not make up for the inconvenience/lack of comfort of a MT).