I have fixed it! It was due to an incorrect gateway in my ESPHome Secrets yaml. I had it as 192.168.10.1 (as that is what my router is), but it should be 192.168.20.1, as it is on vlan 20! Thank you so much for all of your help!
EDIT: ESPHome over VLAN became unreachable - #5 by Ronaldt helped me out as well!