Your experience is consistent with a scanning problem that began after updating to macOS Sequoia 15.7, although that does not establish that macOS 15.7.9 is the cause.
One important point is that Canon's current support page for the PIXMA MG5720 does not list the model as compatible with macOS Sequoia 15 in its operating-system compatibility table.
Canon does, however, provide software and driver downloads for different macOS versions, so it is worth checking exactly what Canon currently offers for your MG5720. (Canon USA)
Before making any major changes, select the MG5720 in Apple menu >> System Settings >> Printers & Scanners and see whether Open Scanner is available.
Apple explains this here: Scan images or documents using a scanner and your Mac.
Also open Image Capture and see whether the MG5720 appears under Devices or Shared.
Apple specifically supports scanning through Image Capture and recommends checking the manufacturer's software if the scanner does not appear. (Apple Support)
Because Sequoia introduced additional controls for applications communicating with devices on the local network, check System Settings >> Privacy & Security >> Local Network.
If Canon scanning software appears there, make sure access is enabled.
Apple documents this setting here: Control access to your local network on Mac.
Apple also notes that macOS Sequoia requires third-party applications that interact with devices on a user's local network to request permission. (Apple Support)
Most importantly, I would check Canon's MG5720 support page for the currently available scanner software, rather than assuming that the older scanner software already installed on the Mac is appropriate for Sequoia.
Canon has previously advised MG5720 users on newer versions of macOS to use IJ Scan Utility Lite when the regular scanner driver was not available. (Canon Community)
I would not conclude at this point that either the scanner has failed or that macOS 15.7.9 is definitely responsible.
The combination of whether Open Scanner is available, whether the MG5720 appears in Image Capture, and which Canon scanner software is currently installed will give us much better evidence about where the problem lies.
If you tell us what you see in Printers & Scanners >> MG5720 and Image Capture, we can then focus specifically on the Canon software/driver issue rather than having you repeat the general troubleshooting you have already tried.
