Not really unless you are driving under about 10 mph very gently. Even then, range in EV mode is very low.
Does the internal combustion engine shut down at least some of the time when you are stopped at a traffic light? If it does then the traction battery is functioning to some extent.
If you are doing a lot of highway driving, you might be noticing that the hybrid version of the RX doesn't get much better gas mileage than the regular RX.
From the 2008 RX and RX hybrid sales brochures:
RX:Fuel Consumption 18/23 mpg (FWD)19
(estimated city/highway) 17/22 mpg (AWD)19
RX Hybrid: Fuel Consumption 27/24 mpg (FWD)
(EPA estimated city/highway) 26/24 mpg (AWD)
EPA fuel consumption estimates are widely seen as fantasy. We've rarely achieve EPA estimates on our vehicles. For example, my wife's 2012 Prius v hybrid - owned since new - has been averaging only 32 mpg in mostly city (35 mph to 45 mph) driving. It's EPA city/highway estimates are 44/40 mpg. Of course, the battery in her Prius is over 7 years old and might be getting weak although the car has only 43,000 miles on it. Her low city fuel economy could be related to her rarely driving more than 15 miles/day and there aren't many traffic lights or downhill slopes that would trigger regenerative braking on the routes she takes. Traction battery charging is totally dependent on regenerative braking.
I have to assume that a Lexus dealership could test your traction battery and the regenerative system for health.
If your traction battery is weak and you want to replace it, there are several companies that sell re-manufactured ones ... like: https://greenbeanbattery.com/lexus-rx400h-hybrid-battery-replacement/
A traction battery supplier like Green Bean Battery should be able to tell you if traction batteries for new model years can be used in your RX.