How to connect the mouse without a mouse

Borrow or buy an inexpensive USB keyboard and mouse set. Always good to have these around even if the wireless devices work.

I am having a similar issue. Mac Mini M4 with old Apple BT keyboard and old Apple Trackpad. The setup initially worked on first turn-on, the bluetooth assistant came up as expected to allow pairing.

But with macOS 15.3.2, I cannot make that automatic pairing come up anymore. If you lost a pairing or had to reset it fro certain reasons, you are left dead in the water. So either this only works once during initial setup, or Apple changed something in the later OS releases. I find it annoying and fault Apple.

Yes it is a good idea to have wired emergency accessories, but for a "headless" system like a Mac Mini, bluetooth pairing needs to be more robust. Since the auto-assistant did work at some point, we are dealing with a (new?) software issue?

Please get yourself a third party USB keyboard and mouse. You may need to only charge the keyboard and mouse however as you have not provided us with much information it is difficult to troubleshoot.