I suppose that this is one of the most typical doubts when someone starts looking for info about blockchain and cryptocurrencies. The question is simple and the answer is simple too, but until you ask it it is not so obvious.
We never trust companies that say we should keep our BTC in their custodial service, because that is exactly the opposite of what everyone should do. Any non-custodial crypto wallet that is also open source will be a good choice, whether it's about generating a backup through a seed or extracting a private key that you will then store safely, preferably in multiple copies.
Never trust companies, because they are only there for profit, proven countless times and will continue to be proven in the future.
The eternal dilemma: on one hand, if you keep it in a third party's custodial service, then you have to trust on him, but you should know that one of our mottos is "don't trust, verify". On the other hand, if you custody yourself your keys, you are responsible for their destiny and you won't be able to blame on anyone if you lose them and your coins get lost forever.
At least, in the case mentioned (if the wallet company closes), you will be safe and able to introduce the seed in another wallet of your choice.