"Assuming (!) the printer requires 300 PPI native resolution, then you'd need to upsample by a factor of 300/23.368 = 12.838x "
Can I assume that that 12.838x (7360 × 4912)px? Or am I missing something? Many thanks
Yes, if treated as a single file it becomes 94488 x 63060 pixels (6 GB at 8-bit/channel). A regular TIFF is limited to 2 or 4 GB maximum, so a Big TIFF or other file type needs to be used, or the resampling result must be fed directly to the print pipeline. One can of course do several things about that.
One thing is to not upsample to the native resolution of the output device. But that leaves part of the resampling to the output driver / RIP, and it changes any output sharpening done to the smaller size output file.
Another thing is to do the correct upsampling and output sharpening at the native output size, but subdivide the image in tiles. Depending on the printing process those sections can then be recombined at printing time, e.g. by printing the sections edge to edge, or first composite them to a single file before printing, but that depends on the RIP or printer driver's capabilities.
The capabilities and preferences of the printer operator will dictate which route to take. Also the mounting method, single image, panels, banners, frames, support materials, transportation method, etc., etc., all play a role.