Electrum wallet is an SPV wallet, the synching should take nothing more than a second or some seconds.
Electrum can be quite slow when syncing many transactions. You can try this for yourself by importing an old watch-only address.
The large number of transactions may be the reason Blockchain's (buggy) wallet doesn't show the deposit anymore. OP should probably consider switching to a new wallet, and create a new seed phrase for that.
would like to send you a small Tip on BTC for the time and great explanation
Many users have their Bitcoin address in their profile. Click his username to find it.