Car would randomly struggles to crank over?

The past 2 weeks my car would randomly struggle to start/turn over. Maybe nothing longer than a solid 4 seconds, but it's an obvious struggle. It's only the first start of the day. Once I drive it and stop somewhere- it starts just fine the rest of the day.

I just bought a new battery for it 3 months ago. Thought it might have been a faulty battery and went to get it tested. Battery is 100% fine.

Took it to Advanced Auto and they tested (but didn't show me the screen) and said everything was fine. Didn't get a great vibe from the person helping me so I took it by the AutoZone on my way back home just for the hell of it. They tested and showed me the screen and it said Voltage Regulator Failed/ Diodes Passed. Figured it may be the alternator or voltage regulator.

I scoured the internet and decided to do a little mini test and I unplugged my interior led lights that are USB connected (maybe I got a bad set that's draining something? Idk) but when I tried to start my car the following 2 days. It starts just fine.

Day after that, it struggles to start again. I take it to a different AutoZone near work and he shows me the screen, and everything passed this time (?) I'm stumped.

Car starts just fine today. I had an oil change scheduled at Meineke and my car was given a full bill of health. (Although I'm not sure how deeply they examine the car in their full-point check) but regardless. I still have no answers. Mentioned the issue to them and they loosely suggested it could be the starter going bad (however everything I've read about a failing starter wouldn't even allow the car to turn over).

Help?