Sequoia installation error

Hello, I have a Mac OS Catalina 2013 that I successfully upgraded to Sequoia about a year ago.

Up until now, everything was fine, until I realized I had forgotten to disable automatic system updates.

This has caused some lag for the past few days.

So, I disabled this this morning and then ran the OCLP root patch.

After more than an hour of installation, it got stuck for another 30 minutes at a step, and suddenly my Mac started making a terrible noise.

I made a huge mistake by pressing the "shutdown" button in the top right corner of the keyboard...

I haven't been able to start it since.

I don't know what to do, especially since I no longer have the OCLP installer on my USB drive that I used to install Sequoia. How can I fix this, please?