The method for turning off Automatic system updates in Developer options in the article linked by @SuperT works on a household Moto G6 Play (as close as I’m able to come to a Moto G7) running Android 9 Pie. As your G7 is currently running Pie, I expect it would work on your phone as well.
That said, I’m unconvinced Motorola will respect that indefinitely. Manufacturer’s work very hard to keep their phones updated (while they’re offering updates). They do so because of the security implications of running older software. I appreciate where you’re coming from and the method is certainly worth a shot. Hopefully, it will, at least, buy you sufficient time to assess Android 10. For what it’s worth, I’ve had multiple phones running Android 9 Pie update to Android 10. A10 is by no means a radical change from Pie.