It can be difficult to put the mouse over the right place to highlight and select a component.
It seems that objects can only be selected by clicking exactly on the lines that make up their symbols and not on any spaces in or very close to them.
For example even at 150% zoom, it can be quite hard to find the exact spot to highlight the dashed line around PSU in:
https://easyeda.com/fileviewSingle-stage-NJfet-amplifier_w5ZhbtL3X.htm
The dashed line can only be selected by clicking on the dashes themselves, not on the spaces between them.
Extending the selection area around an object by some number of pixels around the object would help.