CryBaby

You could set up a cron job to reboot it every so often. Log in with PuTTY and type
sudo crontab -e This will open the default crontab in an editor, probably nano. At the end of the file add the line
0 * * * * systemctl reboot to reboot every hour on the hour. It needs to have a newline at the end, ie. a blank line at the bottom of the file.
man 5 crontab will tell you more.

Take the SD card out and put it into another machine. Copy the whole card as an image. To restore you just copy it back. On Linux I would use dd for this:
sudo dd if=/dev/mmcblk0 of=backup.img bs=1M status=progress making sure you have the right dev. It should not be mounted while you do this.
On Windows... Balena Etcher?