Okay, now that's unrelated to the previous issue and not limited to Electrum,
the error: "The transaction was rejected because it is too large (in bytes)" is because of Bitcoin's "standard rule".

Your transaction must have reached the maximum standard transaction size of 400,000 Weight or 100kvB (virtual kilobytes).
You'll have to reduce the number of inputs in order to create a transaction that can be broadcast successfully.
The expensive workaround is to ask a pool or solo miner to directly include your transaction to the blocks that they're mining.

Source Code: https://github.com/bitcoin/bitcoin/blob/master/src/policy/policy.h#L23-L24

After version 4.0.1, electrum dropped support for the old export format and use "psbt" similar to Bitcoin Core.
Here's the release notes: https://github.com/spesmilo/electrum/blob/master/RELEASE-NOTES#L302-L306
The solution is also written there - all co-signers should have the same version or at least v4.0.1

If the raw transaction came from other source that outputs raw transactions in hex.
You can try to convert it into psbt through Bitcoin Core using the command: converttopsbt "raw_transaction", the output should be compatible with the latest version of Electrum. It could fail depending on the encoding of the raw txn.
Note: you wont need the blockchain to use the command, just install, open Bitcoin Core then go to 'Window->Console' or use cli.