Can some of the kata be practiced alone?
Understanding that they are used to transmit feeling, and methods of movement with distance and timing, that is why they are always done in a partnered pair.
Yet, there are some excellent reasons to practice some of the kata alone/solo so one is better prepared when time is available to partner up.
A few training points to consider.
Looking at the patters, some are better suited to solo practice compared to others- kata from Koto ryu and Gyokko ryu are better for this compared to Kukishinden ryu. Sections of Shinden Fudo ryu work.
The aim of practicing alone is to slowly review the mechanical movements.
Work on the movement steps of the kata to become familiar with them.
Work on balance by going very slow and paying attention to the knees, hips, and spine.
Use them as a form of training to build up the legs by getting as low as possible, and moving low from that position.