GPS was the first Global Navigation Satellite System (GNSS) and the term GPS is often used as a synonym for GNSS.

Older software often only checks for NMEA 0183 sentences starting with "$GP" (= GPS only) instead of looking for all GNSS systems.

Newer GNSS receivers often use multiple GNSS systems and therefore "$GN" is used ("$GNRMC...") if it recives a combination of GPS, Galileo and GLONASS signals.

It would be better to us instead of "$GPRMC" either "$G.RMC" (“.” = anychar) for using GPS, Galileo and/or GLONASS (GNSS) or even "$..RMC" which means any source.

NMEA 0183 sentence "$XXYYY..." explanation:

"$" = Start 
"XX" = Source device (https://de.wikipedia.org/wiki/NMEA_0183#Ger%C3%A4te-IDs)
	BD = Beidu
	GA = Galileo
	GL = GLONASS
	GP = GPS
	GN = GNSS position fix from more than one constellation (eg. GPS + GLONASS)
"YYY" = Record
	RMC = Recommended Minimum Sentence C (used in most cases)
	GGA = Global Positioning System Fix Data
	GNS = GNSS fixed data
	GLL = Geographic Position - Latitude/Longitude
	...

Source: https://de.wikipedia.org/wiki/NMEA_0183

gps2serial-gnsstogps.are

    /* DESC: This script sends the local GPS NMEA stream to the serial interface.
    * DESC: It checks for the correct CR/LF end of line characters and convert messages $GN to $GP 
    * Copyright (C) 2013-2021) NetModule AG, Switzerland
    */
     /* Options to configure by user*/
    SER_SPEED = (int) argv[2];	/* Serial Baud Rate 4800, 9600, 19200, 38400, 57600, 115200 */
    SER_DATABIT = 8;	/*  number of data bits (5, 6, 7, 8) */
    SER_STOPBIT = 1;	/*  number of stop bits (1, 2) */	
    SER_PARITY = 0;		/* parity (0=no parity, 1=odd parity, 2=even parity) */
    SER_FLOW = 0;		/*  flow control (0=none, 1=xon/xoff, 2=hardware) */
    DEV = "SERIAL1";	/*  name of the Serial Interface */
 
    /* default values */
    local_ip = "127.0.0.1";
    local_port = (int) nb_config_get("gpsd.0.port");
 
    gpsd = -1;
 
    // start serial connection
    int start_serial() 
    {
    	if (nb_config_get("serial.0.status") != "2") {
        	nb_syslog("serial not assinged to SDK\n");
            exit(2);
        }
        // printf("set serial attributes\n");
        if ((rc = nb_serial_setattr(DEV, SER_SPEED, SER_DATABIT, SER_STOPBIT, SER_PARITY, SER_FLOW)) != 0) {
            nb_syslog("ERROR: unable to set serial attributes (rc %d) to %s\n", rc, DEV);
            return -1;
        }
        // nb_syslog("Open serial device %s\n", DEV);
        if ((fd = nb_serial_open(DEV)) < 0) {
            nb_syslog("ERROR: can't open serial port %s\n", DEV);
            return -1;
        }
        return fd;
    }
    // restart GPS deamon
    int gpsd_restart () 
    {
    	nb_syslog("Restarting GPS daemon");
 
    	nb_config_set("gpsd.0.status=0");
                    do {
                                    sleep(3);
                    } while ( nb_config_done != 0)
 
    	nb_config_set("gpsd.0.status=1");
                    do {
    	                sleep(5);
                    } while ( nb_config_done != 0)
    	return 0;
    }
 
    // start TCP Socket for GPS deamon loop 
    int gpsd_connect ()
    {
    	nb_syslog("Connecting to GPS daemon");
 
    	gpsd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    	if (gpsd < 0) {
    		nb_syslog("ERROR: Unable to open socket");
    		exit(-1);
    	}
    	for (attempt = 0; attempt <= 15; attempt++) {
    		sleep(15);
 
    		if (connect(gpsd, local_ip, local_port) < 0) {
    			nb_syslog("Could not connect to daemon");
    			if (attempt == 12) {
    				nb_syslog("Unable to connect, restarting daemon");
    				gpsd_restart();
    			}
    		} else {
    			break;
    		}
    	}
    	nb_syslog("Connected to daemon, requesting NMEA");
    	send(gpsd, "R=1\n");
 
    	nb_syslog("Processing NMEA");
 
    	return gpsd;
    }
 
    string checksum(string s)
    {
    	pos = strchr(s, "*");
 
      	if (is_void(pos))
    		return s; /* no checksum to correct */
 
    	cs = 0;
    	chars = explode(s);
            for (i = 1; i < pos; i++) { /* skip $ and *XX */ 
    	    c = ord(chars[i]);
                cs ^= c;
            }
            r = sprintf("%s%02X%s", substr(s, 0, pos + 1), cs, substr(s, pos + 3));
    	return r;
    }
 
    /* main() */
 
    if (argc < 2) {
        usage();
    }
 
 
    /* starting serial */
    nb_syslog("starting serial");
    if ((serial_fd = start_serial()) < 0 ) {
        nb_syslog("Could not start serial, exiting\n");
        exit(4);
    }
 
 
    /* process NMEA stream */
    nb_syslog("Processing NMEA data");
    while(1) {
    	/* connect to gpsd */
    	if(gpsd < 0) {
    		gpsd = gpsd_connect(gpsd);
    		if(gpsd < 0) {
    			nb_syslog("ERROR: Unable to connect to daemon");
    			sleep(5);
    			continue;
    		}
    	}
 
    	/* wait for client socket data  */
    	rv = select(gpsd, 3);
 
    	if(rv == -1) {
    		nb_syslog("ERROR: select failed, re-connecting");
    		close(gpsd);
    		gpsd = -1;
    		continue;
    	} else if(rv == 0) {
    		/* nothing received */
    		continue;
    	}
 
 
    	data = recv(gpsd);
    	len = strlen(data);
    	/* Check for correct framing: CR+LF */
    	if(len > 2) {
    		if(strrchr(data, "\r") != len-2 || strrchr(data, "\n") != len-1) {
    			nb_syslog("ERROR: NMEA framing wrong");
    			close(gpsd);
    			gpsd = -1;
    			gpsd_restart();
    			continue;
    		}
    	}
 
    	if(len == 0) {
    		nb_syslog("ERROR: no data, re-connecting");
    		close(gpsd);
    		gpsd = -1;
    		continue;
    	}
    	/* Convert message $GN to $GP for backward compatibility */
    	if(strstr(data, "$GN") == 0) {;
    		a_arr = explode(data);
    		a_arr[2] = "P";
    		data = checksum(implode(a_arr));
    	}
    	/* skip all messages different from GPGGA 
    	* if(strstr(data,"$GPGGA")==())
    	* continue;
    	*/
    	sent = write(serial_fd, data, len);
	   nb_syslog("sending Data via serial interface");
    	  if (write(serial_fd, data, len) != len){
           nb_syslog("Unable to send message via Serial, data %s, len: %i\n", data, len);
	  }
    }
 
    close(gpsd);
    close(serial_fd);
    exit(6);