These are movements I would use with clients in person, they have low learning curves, are biomechanically effective, and can be done without complicated setups.
Heels Elevated Back Squat
This is still my favorite movement for Overall muscle gain, and almost anyone can do it (barring contraindications).
Elevating heels keeps the torso more upright & creates better joint angle alignment at the knee and hip.
You can use 5lb plates under the heels, or the newer wedges.
Versatile and works for everyone, develops the glutes, hamstrings, and quads.
You can use one hand to balance & increase stability, you can elevate the heel, you can load with a barbell, dumbbells, weight vest, kettlebell.
Upright Leg Press
Yes a machine, get over it.
The 45 press I don’t care for, the but upright leg press is super stable, much better joint angle for loading, 100% builds muscle, any level of client can use it, can be emphasized for quads or glutes.
Seated Leg Curl
Yes, another machine, get over it.
Nothing works hamstrings better than a seated leg curl.
My preferred deadlift if I am having clients deadlift, lower back/glutes/hamstrings all worked simultaneously.
Typically I’d start people with DBs, then once they get to 1/2 bodyweight, switch to barbell.
This is a great test of balance, and muscle builder as well.
I don’t care to add much weight, 1/4 of BW enough if you are going to load the movement.
I also never load with weight overhead. Stupid and adds nothing to the exercise.
Bulgarian split squat
These are fantastic because you can load the work leg heavier and with a greater ROM than you often can with a regular squat.
Start with Bodyweight, these tend to produce serious soreness your first time doing them.
I’ve talked about these many times. They train the quads as thoroughly as a bodyweight extension would, they also are a great foot/ankle exercise and require balance as well.
Ideally they should be done for high reps.