Bluetooth not available in 10.14.3

If clicking the mouse or pressing a key doesn't wake the computer, you might need to allow wireless devices to wake up your computer:

1. Choose Apple menu > System Preferences, then click Bluetooth.
2. Click Advanced.
3. Select the checkbox next to Allow Bluetooth Devices to wake this computer.

see > Using a Bluetooth mouse, keyboard, or trackpad with your Mac - Apple Podpora

This may be due to something you have installed on the computer. Please do the following:

Please navigate to the Mac App Store and download the free version of EtreCheck OR please click www.EtreCheck.com where you will find the app. Once you downloaded the free app and created the report please post it as your reply to this post. In order to post it, please use the following link for more detailed instructions on how to correctly post the results: 

https://discussions.apple.com/docs/DOC-250000211

We can then look for obvious issues that may be causing your problem.

If the reports does not show anything obvious there are other troubleshooting steps to take.

Sort of alchemy, but press the spacebar on the keyboard once, and then click once on the Magic Mouse 2. Then wait a few seconds. That is my experience on a 2011 Mac mini with 16 GB RAM, an internal SSD (10.13.6), and one external USB drive enclosure (which also takes extra time to wake up). Same drill on my Late-2013 iMac (Mojave) before it died. No cure, as far as I can tell for the bluetooth delta sleep behavior.