iMac will not connect to mouse and keyboard

If your devices are not pairing or bluetooth is turned off, then you need to use a USB keyboard and mouse to help get then reconnected. FWIW most any USB generic or pc keyboard and mouse will work with Mac's.

also see > If your Apple wireless mouse, keyboard, or trackpad isn't working with your Mac as expected - Apple Support

Mac will not connect to mouse and keyboard I can’t get into my Mac

You need to get and use a USB keyboard and mouse to help get then reconnected. FWIW most any USB generic or pc keyboard and mouse will work with your Mac.