No longer able to mirror objects

I'm still fairly new to blender and the last few days I had been following sculpting tutorials and was able to mirror objects with no problem. But today when I was trying to mirror them it is not working. I also get this pop in the bottom saying "failed to set value". I tried to look up how to fix this but did not get the answer I was looking for and I have even updated to the latest version and I still cannot get the mirroring to work anymore. Any suggestions on figuring this out would be awesome. Thank you so much.

• Try changing the mirror axis, as right now you're mirroring along the axis pointing towards the camera: i.imgur.com/XhqYpx0.png other than that, test if the mirror modifier also doesn't work in a new file. If it works there, you can upload a file where it doesn't work, using this website: blend-exchange.giantcowfilms.com – Markus von Broady Feb 8 at 22:33
• Thank you so much for the help and resources! This helped a lot! – Philosopher Feb 9 at 17:57

Your view is showing $$Y$$ and $$Z$$ axis (Green and Blue lines across the screen respectively), but the modifier is set to mirror only on $$X$$, which would be perpendicular to this view, therefore impossible to see.
You can add mirror in $$Y$$ on the modifier.