The SD card going read only suggests to me either the sd card is dying, or its a fake SD card. There is a scam where for example, bad sellers will sell a hacked 32GB sd card and list it as 64GB and it shows up as 64GB in your device, but when you write more than 32GB to it, it just starts from the beginning of the SD card storage addresses, and overwrites the original files on the device. The end result is, the original 0-32GB is overwritten erased, as it writes the next 32GB of the '64GB' faked total.

If you have the storage space available without the SD card on the new device, I would maybe use syncthing app to transfer the files locally on your own network, from old device to new. If you're handy with linux terminal commands, you could also maybe use rsync to copy the files over your network as well.

It sounds like a dying sd card.

Another idea is: the card may be bigger than the phone supports. This sounds silly, but it's a real problem, the card will partially work but act up if that's the case.

Never used LocalSend. Syncthing is a reliable workhorse that a lot of people use, it works over LAN when possible.