My initial attempt to upgrade from 26.1.11_10 to 26.7 failed with a boot loop: the update process could not go through as it requires several automatic reboots.
1. Removing the Intel microcode plugin as well as AdGuardHome and the community repo did not fix the boot loop.
2. Updating the EFI boot loader as per https://www.freebsd.org/releases/15.1R/upgrading/#upgrade-loader-uefi helped.
3. Now the update went through. Re-installed community repo and AdGuardHome.
4. Yay!