My Bluetooth toggle won't turn on?

Your screenshot indicates that Bluetooth is on. If the resetting of the NVRAM (2 or 3 times in succession) give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

PoohKado wrote:

My magic mouse & keyboard stopped working on my iMac 21.5" 2017 running on macOS Ventura 13.5. I charged them both, Didn't fix. Bluetooth toogle in status bar at top was off, tried to turn on and toogle won't turn on. Went to Bluetooth in system settings turn on toogle & it's blue, but no discoverable devices show up and the BT icon in status bar is still crossed out and toogle switch off. I don't know how to fix?

Did you try the cable connection?

iMac bluetooth external keyboard…

Have you powered off the keyboard and turn it back on?

switching off the keyboard for 30 secs or so and then hard connecting the keyboard via lightning cable and then switching on the keyboard .... then try again your system settings....

no insight—

on Intel you can try resetting NVRAM/PRAM Reset NVRAM on your Mac - Apple Support

on the M1/M2 SoC—

if you have an issue— equivalent Shut down, close the lid 30 secs+ , reboot as normal.

If no resolve try SafeBoot Use safe mode on your Mac - Apple Support to sort anomalies.