Oh I think some of us misunderstood the issue at first. I thought you had successfully installed, but were rebooting back into the installer afterward.
Try using Ventoy. It has been working well for Garuda installs. Quite a few solved threads just from folks switching to Ventoy. ventoy.net
The checksum is a separate file.
Navigate to the folder you downloaded the ISO (cd ~/Downloads for example), then run sha256sum garudablahblahblah.iso and compare the output to the checksum download. If they match you are good to go.