Good afternoon MarkJFisher,
Welcome to the Apple Support Communities!
I understand there is a delay in your Bluetooth keyboard being discovered after waking from sleep on your MacBook Pro with macOS Catalina. The resources below will help you address this issue. I've highlighted some key information here for you. Click the link for complete details.
Using a Bluetooth mouse, keyboard, or trackpad with your Mac
"Connect to Bluetooth devices after wake or startup
Bluetooth devices are usually available a few moments after your Mac completes its startup process. After waking from sleep, your Mac should find Apple wireless devices right away. Other wireless devices can take up to 5 seconds to be recognized. You might need to click a button on your wireless mouse to wake it up.
Some Bluetooth devices, such as audio headsets, might disconnect to conserve the device's battery power after no audio or data is present for a certain amount of time. When this happens, you might need to push a button on the device to make it active again. Check the documentation that came with your device for more information.

Wake your computer with Bluetooth devices
You can click your paired Bluetooth mouse or press a key on your paired Bluetooth keyboard to wake your Mac. You might need to press the space bar on the keyboard.
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:
- Choose Apple menu > System Preferences, then click Bluetooth.
- Click Advanced.
- Select the checkbox next to Allow Bluetooth Devices to wake this computer.

Connect multiple Bluetooth devices to one computer
The official Bluetooth specifications say seven is the maximum number of Bluetooth devices that can be connected to your Mac at once.
However, three to four devices is a practical limit, depending on the types of devices used. Some devices require more Bluetooth data, so they're more demanding than other devices. Data-intensive devices might reduce the total number of devices that can be active at the same time.
If a Bluetooth device doesn't appear in Bluetooth preferences, or if it becomes slow to connect or doesn't perform reliably, try turning off devices you aren't using or unpair them from your Mac.
Fix interference from other household devices
Bluetooth shares the 2.4 GHz ISM band with other household devices such as cordless telephones, wireless networks, baby monitors, and microwave ovens. If you see issues with your Bluetooth devices that you suspect might be due to frequency congestion, see AirPort and Bluetooth: Potential sources of wireless interference for further information."
Take care.