Progress isn't linear and it's also very subjective, so difficult to measure (unless a client is doing more goal-oriented therapy such as CBT). I get the 'hold up a mirror' concept, my T does that too. Often I struggle to see what progress I am making, but she is able to reassure that I have made progress and give examples where that has been the case. It helps to have another person keep track and provide encouragement at times when I feel discouraged.

As for the going virtual over the summer, I'm assuming you will be returning to in person at some point and it's not going to be a permanent thing. I started off with current-T doing all virtual, then moved to seeing her twice a month in person. We now alternate between online and f2f sessions each week. However this is out of necessity rather than choice. I would rather see her in person every week but it's not possible, so every other week is a good compromise. The online weeks are more for maintainence, for issues that are safe to deal with when not working from a safe environment. They help maintain the connection.

Depending on how long the working virtual is going to last for, you could maybe treat these as 'lighter' sessions, not going to deep into difficult stuff, but using the time to do more supplemental work which will underpin and reinforce things when you return to in person.