Illustrator suddenly stopped opening .svg files

I've been opening .svg files in Illustrator for years, and was able to do so all the way up until yesterday, when Illustrator suddenly stopped being able to open them.

Now, when I try to open .svg files I get the following error message:

"The SVG file is invalid. Validate it before opening"

I've read posts concerning this problem, which recommend going into the svg file's code using a text editor to remove unwanted code, or to "optimize" the file using Inkscape.

I am not a programmer and do not know how to edit the code, so I tried the Inkscape method instead.

I downloaded Inkscape, was able to open my svg files just fine, and tried exporting it as every possible type of svg output file possible in Inkscape, including the "optimized svg" format, in which I instructed it to turn off all the metadata, etc.

However, even after doing this, Illustrator STILL refuses to open my newly optimized svg files.

Is there some other output format I can try in Inkscape that will open in Illustrator?

This is really frustrating. I just don't understand why I was able to open svg files for years all the way up until yesterday but that Illustrator suddenly stopped being able to do this.

PS My svg files were created in QGIS.