thnx @jimmo, see the details below:

There apprears to be an issue in the CAN drivers which prevents receiving messages with non extended id's.

As a test I'm using a pyboard-D to send data between the 2 CAN ports.
This works fine when the can filter is set to extframe=True.
can.init(mode=pyb.CAN.NORMAL, extframe=True, prescaler=4, sjw=1, bs1=7, bs2=1)

However, when changed to False, there are no incoming frames detected.
I can see the frames with a CAN bus analyzer, but the rx callback does not trigger.
can.init(mode=pyb.CAN.NORMAL, extframe=False, prescaler=4, sjw=1, bs1=7, bs2=1

I think I might have found where this goes wrong.

I'm using CAN.MASK32 with a blank values like this:
can.setfilter(bank=self.itf-1, mode=pyb.CAN.MASK32, fifo=self.itf-1, params=(0x0, 0x0))

Now when I trace back the code, I come to pyb_can.c, where the filtermasks are set.
They appear to be designed for extended identifier format judging from the high value 0x1FFFE000.

micropython/ports/stm32/pyb_can.c

Lines 710 to 713 in bfbd944

    
           filter.FilterIdHigh     = (mp_obj_get_int(params[0]) & 0x1FFFE000)  >> 13; 
        
           filter.FilterIdLow      = (((mp_obj_get_int(params[0]) & 0x00001FFF) << 3) | 4) | rtr_masks[0]; 
        
           filter.FilterMaskIdHigh = (mp_obj_get_int(params[1]) & 0x1FFFE000 ) >> 13; 
        
           filter.FilterMaskIdLow  = (((mp_obj_get_int(params[1]) & 0x00001FFF) << 3) | 4) | rtr_masks[1];

Now when I change it to blank, I start receiving the packets.
filter.FilterIdHigh = 0x0000; filter.FilterIdLow = 0x0000;
filter.FilterMaskIdHigh = 0x0000; filter.FilterMaskIdLow = 0x0000;

I don't understand the bitwise operators that are applied in the original code, maybe someone can have a look at it.

	filter.FilterIdHigh = (mp_obj_get_int(params[0]) & 0x1FFFE000) >> 13;
	filter.FilterIdLow = (((mp_obj_get_int(params[0]) & 0x00001FFF) << 3) \| 4) \| rtr_masks[0];
	filter.FilterMaskIdHigh = (mp_obj_get_int(params[1]) & 0x1FFFE000 ) >> 13;
	filter.FilterMaskIdLow = (((mp_obj_get_int(params[1]) & 0x00001FFF) << 3) \| 4) \| rtr_masks[1];

Uh oh!

stm32: pyb.CAN.init(extframe=False) excludes all frames #5508

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