In the case i did the choosing BIP39, tried the "Detect Existing Accounts" option, after that Electrum Wallet detected BIP44 Legacy Account 0 providing the evidence for transactions made under Legacy Tab in the Blockchain Wallet, transactions' amounts and dates were correct, would it still be the issue "to sync the "blockchain headers" with the servers before it can display the correct balances" under the Segwit Tab?

"easier way to search addresses is to go to view menu > show addresses, switch to addresses tab, press ctrl+f and paste in the address in question." Thank You for the advise. Does it concern the Electrum Wallet?

"How do you know the addresses you are checking on a blockchain explorer?". I created them myself. I used the correct Blockchain.com Wallet because it is the only one. i sent the Addresses to the Sender, the only ones i created in the Wallet. There is no possibility i could send incorrect addresses because they were the only ones i created. I do not know about the malware issue, but the BTC balance is on the addresses i sent (blockchair.com, etc.,), the balance is "Unspent", amount is correct, and did not disappear anywhere else. i do not know whether it is the evidence or not.
If i go to "Add Next Address" under the Segwit Tab i can create the new address and it is shown under the "Unused Addresses".

I created the 7 of the Addresses because there was a limit for the amount to be transferred by the Sender, so, i did each Address for each amount simply choosing "Add Next Address".

"You can also try that to check if you can reproduce those addresses into your blockchain(dot)com's unused addresses list." Could You, please, send the hint for this to be managed?


Thank You.