Look into the t-series thinkpads. T480 is the meme one, but many newer models are very inexpensive and modular. I don’t have dells, but people who do recommend the Inspiron or Vostro ones. They’re similarly cheap and repairable. There are business class hp laptops for cheap too.
For my needs these computers have been very useful and fast.
Often a whole parts unit (bad screen, no ram, no hd for example) of one of these laptops can be had for the price of a single replacement part from one of the smaller manufacturers.
Because they’re so common, new production third party replacement batteries are available and new old stock as well.
If you value environmentally friendly actions, using these machines is literally taking plastic out of the waste stream.
Probably the best way is to unplug it from the charger and remove the battery.
You can’t effectively use the device while it’s not vulnerable to attack.
What kind of eavesdropping are you worried about? I ask because concern over advertising is different than concern about laser listening (a technology that was available to me in kit form as a middle school student many years ago).
It’s not reasonable to ask how to avoid all eavesdropping because without any context you quickly start wondering if you could recover from being rendered and detained for the maximum legal duration in your jurisdiction.