The Forerunner 245 GPS function of the watch is taking too long to activate.

https://www8.garmin.com/manuals/webhelp/forerunner245/EN-US/GUID-8F933BDD-AE3F-447F-9A06-64C4A3257DA5.html

Have you synced your watch with Garmin Connect or Garmin Express in the 24 hours before you tried the gps?

What is your ephemeris state in Menu - Settings - About - go down until you see something like Ephemeris: Current (and if it's not current, then that's the reason)

If you can't sync via GE or GC the get outside, open gps activity and wait. Even after it gets green, continue to wait for another 10-15 minutes. That should be enough for the watch to collect the necessary information from the gps satellites themselves. After this check ephemeris state again. Should be current and after that try to start an activity again, and it should take less than a minute now. If not then contact Garmin customer support, there might be a hardware fault