Electrum has never changed the derivation path for legacy wallets, AFAIK and it has always maintained backwards compatibility. Each of the seeds has a specific version to recover specific wallets and the fact that the checksum is valid for Electrum probably means that the seed is an Electrum seed.
Are the addresses in your recovered wallet bech32 (bc1) addresses? It is quite unlikely for that to happen.
If I check the BIP39 box and type in any derivation path (I tried planty of them) then Elcetrum
tells me "checksum failed" & once I go ahead and am already in the wallet: go wallet > seed
I can't display the seed.
Where as if I just type in the seed without derivation path, I am able displaying the seed.
Electrum doesn't store the phrases for BIP39 recovery. If the checksum is mismatching for BIP39, then you shouldn't be recovering using it. Any working wallet will not generate a seed that has a wrong checksum, because there'll be no use for a checksum.
Yes it does generate. I wrote it above.
Once I check the BIP39 and type in only followong derivation path: m/44'/0'/0' - then I get different addresses which I have used after I have updated the wallet.
If I don't check the BIP box then it generates the wallet I had after the update.