I think I'm clearly stating my assumptions. GPL3 and LGPL3 requires you to enable the user to replace the GPL/LGPL3 code on your device with the users own version of said code. It does not matter if you link statically.

Now, it would be possible let the user do this and not let it be a problem for your product (in terms of security, reverse engineering, ip theft, etc) but it is more and harder work.

I have used both older version of Qt (LGPL2) without licensing and newer (LGPL3) with licensing in commercial products. The former was not a problem. But using LGPL3 Qt without licensing in a commercial embedded product is a headache (if you are concerned about the problems it might bring), according to me.

Hence, I wish Flutter all the best.