There is an easy, if a little inconvenient way, to add your own POI's and also set up alerts for them.
I use Diskaid, it allows me to add and remove .OV2 and .PNG files.
You need to use .PNG files rather than .BMP as the iPhone app wont work with .BMP
They also need to be 44x44 not 22x22
You can also use the mapsettings.cfg file from something like an old TT GO 740 Live, this allows you to set up alerts for things like speed cameras to trigger at set distances.
You can't edit the mapsettings.cfg file on the iPhone app so it needs to be "edited" elsewhere then transferred to the iPhone.
The iOS app will use .bmp files, I find they still work best at 44 x 44 rather than 22 x 22.
I now use iMazing to manage files on the iPhone, It works very well!