Just look at your Roth IRA statement for the period of time that the conversion was done. It should show a dollar value received by the Roth IRA, not just shares. The 2020 5498 must also show the dollar amount received by the Roth IRA, and it should show as a conversion (not rollover) contribution. You may not have received the 2020 5498 yet as they are not due until May (maybe June this year due to the filing due date extension). If any question, call Fidelity and they can provide the figure. They need it for Form 5498. The confirmations will not provide this info. I would not bother with the 1040 Inst, since you are looking for the gross amount converted, not how to report it. You will need Form 8606 to report your conversion, and what you are missing is the amount to go on line 8 of the 8606.
It is correct that the 1099R forms will not provide a separate conversion amount when there were other non conversion distributions in 2020 from the same IRA account.
Finally, if you have any basis in your TIRA and file Form 8606, the amount on 4b will be less than the gross amount converted because a portion will be non taxable. Form 8606 will show the taxable amount on line 18 if you have IRA basis. If you have no basis (most do not), then ignore this paragraph.