Be careful with those old versions, because I'm not sure exactly which version fixed the critical vulnerability that allowed hackers to send phishing messages through the official wallet. I think it was fixed with version 3.3.4 or later.

I suggest you think about sending your coins to a new wallet (in a transaction) so you have them safely. Before that, I would certainly check whether such a new wallet will generate the same BTC addresses if you recover it with seed. That means installation + verification of BTC addresses (just copy/paste few of them) + uninstallation + installation and recovery of wallet with new seed.

This is not possible.
If you check the  "Extend this seed with custom words", enter your seed phrase and click the "Next" button, you should see a new window where you can enter you custom word.

Where did you download electrum from?

Recover your wallet with these steps.

Wallet with two-factor authentication
I already have a seed.
Enter seed.
Options: choose "Extend this seed with custom words", OK
Next: type your custom words, Next.

Then you will have two options: Keep or Disable.
Keep means you restore your wallet with 2FA.
Disable means you restore your wallet but no longer want to use 2FA.

Keep
Enter your password
Next
Email address
Google Authenticator code
Next to finish the wallet recovery.

Disable
Enter your password
Next
You will recovery your wallet successfully, without 2FA.

If you have extended your seed phrase with a custom word, you must enter the custom word when recovering your wallet. Otherwise, you will generate a completely different wallet.
Click on "options" in "Enter seed" window and check "Extend this seed with custom words". Electrum will ask your custom word after clicking on "Next".

Simply following this[1] and choosing 2FA instead of standard  (which seems like you've already tried) should've restored your wallet.

Make sure you're connected to electrum servers (see if there is a green dot on the bottom right side), and that you're using the latest version downloaded from the official site.

Did you withdraw from an exchange to this wallet before? If so, you should check the address you used on a blockexplorer and see if the funds are still sitting there and then compare that address with what you have in Electrum.

[1] https://bitcoinelectrum.com/restoring-your-standard-wallet-from-seed/