2019 Equinox sat too long, won't start

Are you saying it cranks good but won't start or the starter motor won't even crank the engine? You can use digital multimeter across battery posts, everything off, the generic spec for a full charge is 12.6 volts. If much below that, need to charge. Battery connections all good? With meter leads still touching battery posts, have helper turn key to crank, how much does the reading drop or does it drop at all? have you tried jumper cables or jump box? now, if it cranks good but won't start, then you check the basics, spark--proper fuel pressure--fuel injector pulse--applicable trouble codes. If battery voltage is lost, it can effect your security system. It just depends on what is going on. Just my opinion.