There is time to make a corrective action for 2023, so it's worth checking on all of this.

https://www.irs.gov/pub/irs-pdf/i1099r.pdf

Code G: "Use Code G for a direct rollover from a qualified plan, a section 403(b) plan, or a governmental section 457(b) plan to an eligible retirement plan (another qualified plan, a section 403(b) plan, a governmental section 457(b) plan, or an IRA). See Direct Rollovers, earlier. Also, use Code G for a direct payment from an IRA to an accepting employer plan, and for IRRs that are direct rollovers."

Which typically has nothing to do with from Trad to Roth IRAs, because those accounts are not under a plan. I would start there, then. Was an employer or employer plan involved? Is the broker with the account working under an employer's plan?

And ask for a Form 5498 for tax year 2023 for this destination account, to see what it was labeled going in. The 1099-R is for the outflow, so it isn't always informational to the taxpayer's action.