GNU Radio Companion 3.10.4.0 (Windows - Radioconda installer)
Uniden Bearcat UBC-3500XLT
PySerial 3.5 + Python 3.11.4

I copied pyserial-3.5.dist-info and serial folders from Python 3.11.4 to
C:\Users\<user>\radioconda\Lib\site-packages

Embedded Python block

Embedded Python block code:

import numpy as np
import serial
from gnuradio import gr

class blk(gr.sync_block):  # other base classes are basic_block, decim_block, interp_block

    def __init__(self, comPort='COM4', comSpeed=19200.0, timeout=2):
        gr.sync_block.__init__(
            self,
            name='window voltage',
            in_sig=None,
            out_sig=[np.float32]
        )
        self.comPort = comPort
        self.comSpeed = comSpeed
        self.ser = serial.Serial(self.comPort, self.comSpeed)
        print(self.ser)

    def work(self, input_items, output_items):
        self.ser.write(b'BAV\r')
        b = self.ser.read(8)
        b = b.decode('UTF-8')
        b = b.replace('BAV,', '')
        output_items[0][:] = float(b)
        return len(output_items[0])