Do you believe in Baruch de Spinoza's belief in God? Spinoza was a 17th century Dutch philosopher. He was a realist. The number one question students asked Einstein was "do you believe in God". He answered,"I believe in Spinoza's God".
You seem to be a realist as I am. I a retired research chemist and engineer.
I do not.
I generally keep myself far away from any questions whether (a) G/god exists or not and which shape it would have.
All the philosophical proofs of the existence of a God, be it of Spinoza, Descartes or Acquinas are worthless to me.
I think I said somewhere in a previous post that I like to do my own thinking based on the data. Of course that has its limitations and you have to start from some axioms always. All philosophical proofs do so as well, and their axioms are rarely objective truths even though they'll go a long way in trying to pose them as such. As you say in your questions yourself: "Spinoza's belief", the belief, not an airtight proof or truth.
Nevertheless, the concept of (a) G/god is well-defined in many different ways by people all over the world, past and present. If we look at some of Spinoza's work, God equaling (all of) nature, to simplify it a bit, is not necessarily a far-fetched concept, but it's still a belief. From a technical point of view, if God is defined (axiom) to be "all-knowing" etc, then from a physics point of view, God is everything including all of nature, but also all the galaxies out there as all information is contained within all mass in the universe according to classic physics. So if someone wants to define their God that way, I can agree this is their belief and true if their axiom holds. However, it starts from an axiom that this person wants to define something or someone all-knowing exist. Same concept for all-powerful or all other properties assigned to their concept of (a) G/god.
So while I do not belief in this myself, I do observe that this concept is some people's belief so to say.
However, it's not because a majority or plurality of people belief something that this is necessary the most likely to be true. History has ample (counter)examples of that.
We have to understand that when one has to live in a time where they are constantly confronted with "God", it's hard to imagine a world without and not start all philosophical musings with that starting point in mind.
These days, there are ample ways to explain the existence of religion and belief-systems from an anthropological and sociological lens instead. Animals do not need this to make sense of their lives (as far as we know).
Finally, there is the Bayesian approach to things. The posterior likelihood of something is its prior likelihood combined with the data. Some of the things currently unexplained by science could be hypothetically explained by an "unseen force" which could or could not be something that people may define as (a) G/god. One could make arguments of the posterior likelihood of God/gods of different forms based on the likelihood of events that happened (the data) and the prior they are willing to assign to each of the different explanations. However, this is obviously an intractable problem and would in essence be a probabilistic version of all the same imperfect philosophical arguments.
So, in conclusion, there currently is insufficient data for me to prove the existence of what people call (a) G/god, nor is there sufficient data to reject the idea. I personally, at this stage in life, do not need the concept to give sense to my life, so I find it useless to give it more though. However, I do accept that others have different views and I accept those as beliefs that can be held, not as truths.