The stock market is a terrible - criminally negligent - place to keep a company's operating cash. I would be fascinated to read advice from an accountant or other financial professional that says otherwise.
I once worked at a company which used a money market fund for its cash. That gave them a slightly better return than a bank account. In the end, not sufficiently better to be worth bothering with.
If the company has an excess of cash and nothing good to spend it on, I think it's fine to put it in the stock market. Maybe you wouldn't count this as "operating reserves" - I wouldn't do that with the money that's earmarked to pay suppliers but not due for another month, but I would do it with the money that's earmarked for opening a new business location at an indefinite time in the future.
You can get whatever risk profile you want from the stock market in return for less yield. If you can accept two-nines certainty that you won't lose half your money in six months, any broad index fund will do. That would be acceptable for a lot of "modest businesses" which find themselves with "6-7 figures cash reserves". If you need better, you can do fancy things with options, or put a fraction of the money in the bank and invest the rest.
(I am a financial professional, but not in this field, and this is not financial advice)
I once worked at a company which used a money market fund for its cash. That gave them a slightly better return than a bank account. In the end, not sufficiently better to be worth bothering with.