Most Intel apps run fine, but there are well documented specifics of what doesn't work at all or not so well (this is taken from The Eclectic Light Company, see details there):
What M1 series Macs can’t do
They can’t run any version of macOS before Big Sur, even in a virtual machine, as those are built to run only on Intel processors. Rosetta can’t translate those, nor can virtualisation environments running on M1 Macs run macOS 10.15 or earlier.
They can’t use some app plug-ins that are Intel-only unless the host app is run in Rosetta translation. This is because translation applies to an entire process, including all the code modules which it might load dynamically. T
They can’t run any unsigned native (ARM) code, including command tools.
They can’t use Intel kernel extensions.
They can’t run Intel code which relies on some newer Intel instruction sets and processor features, such as AVX, AVX2, and AVX512 vector instructions.
What M1 series Macs don’t do so well
They don’t run any Intel operating systems easily. For Linux, this is unlikely to be a problem as there are some good distros which run natively on ARM, which can then be virtualised well on an M1 Mac. For Windows, this becomes complicated. Windows 10 and 11 for ARM will run well when virtualised, but not all Windows software runs in those ARM versions, and some vendors are very reluctant to let you know whether this would be feasible. It sets up supply chain problems too: if you rely on a Windows app, which in turn relies on Windows 11 for ARM being able to translate and run it, which in turn relies on Parallels Desktop or VMware to virtualise it, then your reliance has multiple points of failure.
They don’t load third-party Universal kernel extensions as standard. Running an M1 series Mac in Full Security mode prevents the loading and use of all third-party kernel extensions.
They handle external bootable disks differently from Intel Macs. Unlike T2 models, booting from an external disk doesn’t require enabling in Startup Security Utility, but each bootable volume requires ownership and LocalSecurity settings. Apple Silicon Macs have to start their boot process from their internal SSD, and can’t start up wholly from an external disk. Although many users have no problems starting them up from external disks, some report that specific models of SSD don’t work reliably.
