[Treble-Enabled Device Development A/AB ROMS] AnonVendetta:
My instructions don't resize super, only the logical product/system partitions within it.

And I just realized that your system partition is already ext4, if you're currently running LOS. All the gsi files I've seen are built with ext4, not f2fs.

And like I said, the product partition is only useful for the stock ROM, gsis don't need/use it. Assuming that everything is successful, you would take the space from product and reallocate it to system, perhaps allowing you to run larger gsis like Pixel Experience. Maybe still not the largest ones, but bigger than what you can currently install.

Try deleting and recreating product from TWRP fastbootd anyway, it's worth a try.

fastboot delete-logical-partition product

fastboot create-logical-partition product 1

1 is the size I chose, which worked.

And then flash the empty product file I linked:

fastboot flash product C:\Users\Steve\Desktop\product_gsi.img

Replace my path to wherever you placed the file.

If none of these commands fail, then reboot back into TWRP from fastbootd. Check the twrp error log (button in lowest right corner of screen, at the bottom), see if there are errors regarding mounting product. There shouldn't be, since you've flashed a much smaller empty img, albeit one that is valid regardless.

Also, check /dev/block/mapper (in twrp file manager) to see if the unneeded scratch partition exists. Delete it from fastbootd if it does:

fastboot delete-logical-partition scratch

Back in fastbootd, see if you get any fails when resizing system. If you can, push it to the hard limit until you can't resize any bigger.

Use the blockdev --getsz and df -h commands I listed to compare from previous results.

Even though your twrp can't mount the logical partitions, I think resizing might work.

The worst case scenario is that none of this works and you get nothing but fails. In that case, reflash your stock firmware with Odin. Or, make a twrp backup of the super partition before attempting any deleting/resizing. Since your twrp can't mount data partition, you will need to save the backup to a MicroSD, or to a USB drive connected via a USB OTG cable.

Try just once, if nothing works then at least you will know in the future what's not possible for you. I like to push the envelope and do my own tests, that is how we learn. Instead of simply accepting the statements/conclusions of others.

And I hate to get technical here, but I just have to. I don't think you understand the difference between a partition and a filesystem. A partition is a discrete container on a disk (I include the internal storage in mobile devices in my definition of disk). A partition may or may not be formatted with a filesystem. Or a partition can be raw, which means it cant contain files and isnt mountable. Once you create a filesystem on a partition, it becomes usable for file storage, but until then it's raw. Even if raw, it still doesn't mean it's truly empty, it can still contain metadata. ext4 and f2fs are examples of filesystems.

Edit: And even though your TWRP apparently can't read super (and therefore probably can't back it up), there is still a workaround, by using commands. First, connect a device which you can write the backup to. MicroUSB, USB OTG, whatever. Mount it in TWRP. Open a twrp terminal. Then:

blockdev --getbsz /dev/block/by-name/super

It should return a #, the optimal block size. Probably 4096.

Then:

dd if=/dev/block/by-name/super of=<PathToYourBackupLocation> bs=<#FromPreviousCommandHere>

Example:

dd if=/dev/block/by-name/super of=/external_sd/super.img bs=4096

This should work, because dd reads the super partition in raw mode. It doesn't give a crap what filesystems are inside super, and it doesn't matter anyway, to it. No matter if it's ext4 or f2fs or anything else. It will give you a perfect byte for byte backup of your super.

To restore it:

dd if=<PathToYourBackup> of=/dev/block/by-name/super bs=<YourOptimalBlockSize>

Real example:

dd if=/external_sd/super.img of=/dev/block/by-name/super bs=4096

Restoring this should revert any changes and your super partition will be back to its' previous state.