Three full body days or four upper lower days with only 45 minutes each Programming

Counterpoint for full body: it's much more robust to missing sessions. If you skip one of four in an upper lower split, one lift gets trained once that week. If you skip one full body day out of three, everything still got hit twice. With a life that produces a 45 minute limit, missed sessions are probably a feature of your schedule too.

You can make full body fit by rotating: one main lift per session at full intensity, the other two at a lighter back-off, rather than three heavy lifts every time.

Upper lower four days, for the exact reason you spotted: 45 minutes is the binding constraint, and a full body session with three main lifts plus accessories does not fit into it without rushing your rest periods, which is how you turn strength work into conditioning.

A workable shape for 45 minutes:

• lower A: squat 4x5, RDL 3x8, one leg accessory 3x10
• upper A: bench 4x5, row 4x8, one press and one pull accessory 2-3x12
• lower B: deadlift 3x3, front squat or leg press 3x8, one accessory
• upper B: overhead press 4x5, chin-ups 4x max, accessories

That's roughly 40 minutes with honest 2-3 minute rests on the main lift and 60-90 seconds on the rest. Each lift gets hit twice a week, which is plenty at intermediate level.

Save time by warming up on your feet rather than on a machine. Two ramp-up sets on the bar you're about to use does more than ten minutes on a bike, and it gives you back a sixth of your session.

Superset your accessories. Row and press back to back, curl and triceps back to back. Nothing is compromised because they don't compete, and you get ten minutes back per session. Only do it with accessories, never with the main lift.

Neither, run a proper strength program with five sessions. 45 minutes isn't enough to build anything serious.