What is money is, is a problem I have wrestled with all my investing life. After 40+ years I have come to the following conclusion.
You need 2 kinds of money and a spreadsheet to do all the calculations.
Type 1 is money of local exchange. Type 2 is currency of account (which is how you choose to measure your actual profit/loss).
When you buy any asset, you must price it in both the local exchange currency (as a US citizen, that is US dollars), and whatever you choose as currency of account (at the same time).
Example: on Jan 20, 1987, I bought 3 shares of Apple (hobby, I used to collect stock certificates) I paid around $51 USD for them. Say I used gold as the Currency of Account. At the time, gold was around $400 an ounce. So in currency of account, bought Apple at $51/$400, or .1275 oz of gold. The equivalent value of gold (currency of account) is now $2400 (or so) so the basis (the purchase price) is local currency is no longer $51, but 6 times that ($400 x 6 = $2400). Why? If I had bought the same amount of currency of account, it went up in local currency by 6 times. I would have made that profit (in local currency) if I had just bought that amount of gold and stuffed in "under the mattress".
It doesn't have to be gold, it can be anything. It just needs to be something that you consider a long term store of value. The purpose of to wring out the inflation of fiat currencies, while living in a world of fiat currencies.
Is this perfect? No, but it's the best I have been able to come up with over the years. When I was a little kid, the "silver" you got in change really was silver. If you used silver as the currency of account, then the dollar fiat dollar equaled the currency of account if you used silver as that currency of account. Now, silver is 22x (or so) the value in fiat dollars. My parents bought the house I was raised in for $10,000 in 1959. 22x that amount would be $220,000. QED.