Bitcoin Core wallet and Blockchain.com sorry for the n00b question, it's been awhile since I looked into this. I have a Bitcoin Core wallet on my machine with a backup of the wallet.dat. It's been ages since I opened the application, so I've upgraded it and am re-syncing it.
I also have a Blockhain.com account (originally opened when it was Blockchain.info). I remember that on Blockchain.com I could see my BTC amount. I now can't log into to Blockchain.com because my 2FA device changed and support hasn't gotten back to me for days about how to reset it. Googling suggests their support never gets back.
Since I'm not hearing back from support I'm wondering if I have lost control of my wallet funds. Did the action of creating a Blockchain.com/Blockchain.info account mean I have handed over my wallet to the company and lost this BTC?
Did the action of creating a Blockchain.com/Blockchain.info account mean I have handed over my wallet to the company

Yes.

and lost this BTC?

You are wholly dependent on the continuing good-will and competence of the business and its customer support systems and staff.
When Satoshi Nakamoto invented Bitcoin, his famous white-paper said

What is needed is an electronic payment system based on cryptographic proof instead of trust,
allowing any two willing parties to transact directly with each other without the need for a trusted
third party.

I feel too many people ignore this.