Firstly, your profile is incomplete so we don’t know enough about your setup to give targeted advice.
Secondly, although everyone works differently, it is generally best not to import anything directly into an existing drawing. Start a new drawing, import it there, make sure it is suitable for your use, and then save and use as a component. Unless the thing being imported has layers you want to keep, move everything onto Layer 0/Untagged before saving. You might also want to reduce nesting levels, etc.
If you turn off all layers/tags in your main drawing, you should probably see nothing at all, even with Hidden stuff turned on. That is because best practice is to move all groups/components onto dedicated layers/tags. Only raw geometry within those groups will be on Layer 0/Untagged (and nowhere else).