"My understanding is that most brokers do not lend

"My understanding is that most brokers do not lend your shares if they are held in a cash account. Most brokers consider IRAs to be a cash account and will not lend shares in the account. Check with your broker, but I think most operate that way."

I thought that shares held in cash just couldn't be loaned out, period, so I put it to ChatGPC, and it turns out that they can, but you have to authorize it:

Can Brokers Lend Shares from a Cash Account?
➡️ By default: No.
If you're in a standard cash account and you haven’t agreed to anything else, your broker cannot lend out your shares. That’s because:

You're not using margin

You're holding fully paid securities

Brokers can’t “hypothecate” your shares without explicit permission

BUT...

➡️ If you opt into a Fully Paid Lending Program (FPLP): Yes.
Many brokers now offer these programs even to cash account holders, where:

You voluntarily allow them to loan your fully paid shares

They pay you a portion of the interest they earn from borrowers

You retain ownership, but lose voting rights and immediate recall

Examples of brokers offering this:

Fidelity's “Fully Paid Lending Program”

E*TRADE's “Fully Paid Lending Income Program”

Charles Schwab's “Securities Lending Fully Paid Program”

Interactive Brokers' “Stock Yield Enhancement Program”

So in those cases, yes, a cash account can be a source of loaned shares — but only with your consent.