2020 yz250f Hard to Start

The battery might be bad if it hasn't been taken care of properly ie, bike has been standing in the garage or dealer floor for long periods of time without regular charging.

But the stock Yamaha battery is weak, even when it's a fully functioning unit.

For my brothers 19 yz250f. We have a procedure that we kinda follow. When you first get ready to start the bike, hold the button for 2 seconds of cranking then stop. Wait 5 or so seconds. Then press again for 3-4 seconds. Usually by the 2nd or 3rd time of cranking the bike it will start. Did it last weekend when it was 45°F out. First button hit is to gently warm/wake battery and build fuel pressure. Then the bike starts the next time. Same with my Honda 250. Wake the battery, prime the fuel lines, then it starts. The colder the weather/battery is, the longer it takes for the bike to start.
Lithium batteries need to warm up before they have decent cranking power, so cranking the bike for 2-3 seconds at a time with a small break inbetween helps them warm up. (Cranking too long at a time can be bad as lithium batteries discharge really fast and can damage them)
Still running OEM batteries on both my 19 yz250f and 19 crf250r, both are said to be garbage. Still strong but I also have them on a tender when not in use.