What are the trading restrictions, if any, when investing within my Health Savings Account (HSA)?

I wonder whether there any trading restrictions when investing within my Health Savings Account (HSA).

https://www.loyola.edu/-/media/department/hr/documents/benefits/health-wellness/medical/hsa-investment-faq.ashx?la=en says:

Q: Are there any trading restrictions when investing in mutual funds within my HSA?

A: Yes, there are some restrictions to be aware of when investing
in your HSA. You can only make one BUY transaction per active
trading day. You can only place a SELL or REALIGN transaction
when you have no outstanding SELL or REALIGN transactions
that are Pending or In-process status (see Figure 8).

But this only pertains to mutual funds and is perhaps specific to Bank of America.

The trading restrictions are whatever the plan administrator says the restrictions are, within the bounds of the law. Therefore, let’s focus on the bounds of the law.