Bluetooth will not turn off

Try resetting to factory, might fix. Do not involve Time Machine at any point during the process. Backup and restore known important data files like jpegs, docs, PDFs etc., manually, and re-install apps afresh.

Then the issue is not that BlueTooth is on, the issue is the computer is too slow and that is what you need to address. To begin, please do the following:

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate towww.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community It is helpful to us if you download the report to your Desktop.

Why exactly do you want to turn it off? It creates no harm by simply leaving it alone.

I also use USB powered keyboard and trackpad (I don't use a mouse, just prefer a trackpad) I rarely if ever use BT for other devices but I occasionally use BT for connecting my AirPods. So for the most part, it just sits there in the background doing nothing as nothing is demanded of it.