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);