Unable to left click using touchpad or external mouse

I've got a 2013 15" Macbook Pro running Big Sur. Everything has been mostly OK, however recently my left click has stopped working.

I thought that this was maybe an issue with the trackpad, however when connecting a USB or bluetooth mouse, I am still unable to left click.

I've disabled the trackpad by enabling mouse keys, and then disabling the trackpad when mouse keys is on, however the external mouse still cannot left click.

The only way I've managed to be able to left click is by installing Unified Remote, and then controlling the mouse from my phone.

I've done SMC and PRAM resets with no effect. One thing I have noticed though is that if my Macbook goes to sleep, it will randomly wake up which does suggest an issue with the trackpad. What I'm confused about though is why external mice cannot left click, even with the trackpad disabled.

I've tried booting into diagnostic mode, and it appears the trackpad is also unable to click in here too, hence suspecting hardware issue, but still confused why external mice cannot click with the trackpad disabled, but a virtual mouse is OK

Any ideas?