@huiswerk2
It's your EOOD and your (indirectly, for the purists) money, so you can spend it however you wish! :-)
And certainly companies everywhere use their funds to pay for both expenses and assets/productive investments, and then hold any surplus as fairly liquid assets (cash in bank, CDs, brokerage accounts, etc.). It's not so different from buying some gold, or purchasing your factory (instead of renting it).
However, while it is possible, I don't think it would be very convenient to buy physical gold (stored in your office, perhaps), and itemize it separately on your balance sheet. As @GB_2_BG says it's much easier to open a corporate brokerage account (e.g. Etoro, Saxo Bank, etc.) using your EOOD. And then show your brokerage balance on your balance sheet. Of course, in this case, you don't (usually) buy physical gold, but gold derivatives, or shares in gold-mining companies, etc.
Here's a little page from Etoro on Gold trading:
https://www.etoro.com/trading/how-to-buy-gold/
Tax-wise, I don't think there's likely to be a tax advantage doing it via your EOOD, rather than your personal name. Unless your EOOD is a low BG tax payer, and you are a high NL tax payer. But I'm not a tax expert by any means. If your gold holding is not a one-off, but part of using your EOOD for both trading and investment purposes, then perhaps you can treat yourself as an employee or trader and get a bunch of expenses (office, computers, phones, internet, pension, private health insurance) allowed. But increasing your expenses only helps if you have income to offset, and your investment gold is closer to a less-liquid form of cash, than to a productive income-generating asset.
I like companies, and they can be very useful. But they have a bureaucratic and cost overhead which I'd prefer to avoid, if possible. So if I found myself with a spare EOOD, and I didn't know what to do with it... I'd probably do nothing with it, and likely close it. If I had the EOOD because I'd purchase some Bulgarian real estate (unlike you, I'm non-EU), then I'd double-check the implications about changing my EOOD from an inactive one-asset company, into a more active multi-asset company. My guess is that the recommendation would be to keep an inactive EOOD for my home, and have a second EOOD for trading/business purposes.