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Using mostly machines is fine, don’t worry about what others think is optimal. The truth is, if you push yourself hard, you can get great results regardless of the equipment available to you (and you still need to push yourself hard with free weights too).

Machines trick you into thinking you're progressing. The first time I went from Smith machine squats to free weight squats, I couldn't walk the next day (went from 150kg on the machine to 80kg free weight).

I just don’t think my knees could handle squats. I was thinking to do a leg press with lower weight. Like 20 reps.

Have you looked into isometric weight training? Heavier weight, lower reps, static holds for longer duration. Typically used in physio for rehabilitation but can also work as exercises on their own, especially when you get older and have joint issues.

With good form, your knees shouldn't be involved that much: https://exrx.net/WeightExercises/Quadriceps/BWSquat - your knees shouldn't go past your toes.

fwiw high weight + low reps (4-6) if you want to get stronger, lower weight with more reps for getting bigger (8-12)

Not optimal, but there must be some program for those cases