For those that don't want to pay for/use Tasker, you can run a script in Terminal instead.
Creating a script file in Android OS:
In X-plore (or use what ever file manger you want), go to Internal shared storage "/sdcard". Make sure you are on the root of the sdcard.
In the middle option pane touch "New text file" and a file namer will pop up. Save name as "switchsd.sh" (without the quotations).
Enter the following:
chmod 777 /mnt/switch_sd
mount -o bind /dev/block/mmcblk0p1 /mnt/switch_sd
mount -o remount,rw /dev/block/mmcblk0p1 /mnt/switch_sd
echo "Fat32 mounted"
Hit save in the upper right and exit app. (This will be the script file)
Go to the built in LineageOS Terminal emulator and type the following commands.
mount -o rw,remount /system
cp sdcard/switchsd.sh /system/bin/switchsd
chmod 555 /system/bin/switchsd
This moves the file to your system/bins folder so you can easily run the script without entering a path.
Now in Terminal emulator run the script by typing, "su" to change user. Then type "switchsd" to run the script, wait a sec and it should now say "Fat32 mounted".
Walla! Enjoy. Do this every time you boot into Android.