mac OS Ventura upgrade caused issues with my Seagate external hard drive?!

You mention connecting it to a PC -- that means it must be formatted to be PC-compatible. If you are using NTFS on the drive, that requires a driver which has to be installed on the Mac(s). Those drivers often need to be updated to work with an updated MacOS. Or any external drive firmware or driver -- this is the vulnerability of using such third party tools, one needs to check for compatibility before updating the MacOS.

If this is the issue, after you perform the update to the NTFS or other driver/firmware, the drives should work.

Yes, you will need to install the latest version that is Ventura compatible. I know that Paragon offers such a product, I suspect there are other suppliers as well. I don't use NTFS myself but I have read that one must obtain the paid up version for full functionality. I think the cost is relatively low (like ~ $20) for the paid up version. I believe there may be other options in the App Store as well, or you can find other brands online.