I would clarify that the concept of non-custodial in relation to the Blockchain.com wallet cannot be taken as truth simply for the reason that in the early period of their work before 2016, many users constantly had issues with their own encoding and seed phrase, which was good only for their own wallet. This seed phrase was non-standard and could contain 17 or 19 words.
You are right about blockchain.com wallet old seed phrases. The seed phrases generated by blockchain.com before their upgrade in 2016 were not standard and they couldn't be imported in other wallets. But OP could import the seed phrase in electrum and that means it's BIP39.
In any case, this is a disgusting service and you should never contact it at all.
You are right. Any close-source wallet should be avoided.
nc50lc gave me i found out that on blockchain.com i have 2 btc addresses and the address with 0.15 btc is bc1qmsm9ga2ct7ma7m6854jc7kx54a6300vsekh8g3 with a balance of 0.15 BUT when i click on it the balance shown is 0.
This address is empty and it never had 0.15 BTC. It received 0.01304421 around 6 months ago and that was spent on July 1.
The transaction in which the 0.013 BTC was spent from bc1q.....8g3 contains some other sending adresses too.
The address 19cLH6wxWsWzZfZqyUq3FctW9CXCrYJM1V which is a legacy address was first used in 2018.
When did you create your wallet on blockchain.com?
Did you check your addresses on "Legacy" tab?
Did you try clicking on "Detect existing accounts" after enterting your seed phrase on electrum?