Downgrade from Big Sur to Mojave

Not possible. The Apple Silicon M1 came preinstalled with Big Sur and can not be downgraded to any version of macOS older than Big Sur.

Aside - even if one attempts - Catalina , Mojave or High Sierra could not run the the new Apple Silicon M1 based on the ARMS chip instructions. Catalina , Mojave and High Sierra is written for Intel CPU Only instructions.

Edit: oh, you have M1 Mac which is Big Sur or later only.

Download the Mojave full installer with Safari, backup, make a bootable Mojave USB flash installer, boot it, reveal and erase the whole internal device (not just volumes under it) as APFS (GUID) and cleanly install Mojave to the internal disk, restore from the backup.

https://support.apple.com/en-us/HT211683

https://support.apple.com/en-us/HT201372

Oh, and Photoshop CS6 installer needs a workaround to install on Mojave and its updater does no install all little updates. But basically it works OK in Mojave.

A SSD is highly recommended for APFS because it is slow on HDD. Or install High Sierra and use MacOS Extended (GUID) on a spinning HDD disk.

You cannot downgrade an MBA M1 to Mojave or High Sierra.

Macs cannot downgrade to an older OS than the one they came preinstalled with.

An M1 MBA would have come with either macOS Catalina or macOS Big Sur preinstalled.

Welcome and thank you too :-)