SIM numbers (ICCID) can have variable lengths, and certain modems like the SIM7000 will append an F at the end of the ICCID to accommodate this. This occurs because those modems fill an internal buffer with all Fs for each octet in memory and don't drop remaining Fs once the ICCID has been read. Seeing an F at the end of your ICCID does not affect the performance of your SIM.
Having said that, all Hologram systems use the SIM number printed on your SIM card. If your modem appends an F and you want to use the modem derived ICCID you will have to make sure that the extra F is dropped when using it with Hologram systems like the Dashboard or the Rest API.