How to transfer SMS from old phone to FP3 via SIM card?

I would like to copy some important SMS from my old phone (no smartphone !) to my FP3. I copied the messages to the SIM card and I use the same SIM card in the FP3. Unfortunately, I don’t know how to access the messages saved on the SIM card for viewing/copying. Do I need a special app for that purpose ?

I think I have bad news for you.
I came from a feature phone to the FP2, like you to the FP3, and my FP2 wouldn’t even recognize the contacts that I had saved on my SIM card, because my old phone was to old. In the same way, it is very probable that you won’t be able to import your SMS to your FP3, and that you will only be able to view them on a similar phone as the one you had. Even to copy SMS between smartphone you have to use an app (or perhaps the google services can do that, I don’t know I don’t use them).
How old was your phone? Which model was it?

Or perhaps there is a method for importing SMS from a feature phone, but I haven’t heard about it. Someone may tell you, but I doubt it exists.

I don’t run the stock OS, so I can’t test the stock Messages App, but if messages on the SIM card are logically handled the same way as contacts on the SIM card by Android, then an import function could be somewhere in the Messages App.

If not … I did a quick internet search, which didn’t give me much, but
SMS Backup & Restore was mentioned here and there.

Else … Usually MyPhoneExplorer is pretty good with finding stuff in different locations on the phone, and if the messages could be found, then they could be copied, too.
But I can not test right now whether it can see SMS messages on the SIM card.
How to get it going would be here …