The "new" rEFInd indicates the location of the "old" one as:
Boot EFI\refind\refind_x64.efi from EFI system partition
Boot into Pop_OS and run sudo efibootmgr -v. Note the BootCurrent: line identifying the number of your current boot option, and read the BootNNNN* line with the corresponding number. That line should tell you the PARTUUID of the EFI System Partition (ESP for short) used to boot the system, and the exact pathname of the "new" rEFInd within it. Use lsblk -o +PARTUUID to find out which disk the PARTUUID maps to. If you can't make sense of the outputs, please edit your question to add the outputs of the two above-mentioned commands to it.
I would guess that the "new" rEFInd installation has been customized by Pop_OS and is not located at \EFI\refind\ directory within the ESP, but in a distribution-specific directory like \EFI\pop_os\ or something. Alternatively, the Pop_OS installer might have created a second ESP.
Typically, the installation of a bootloader is a two-step process: first, the regular installation of the bootloader package will provide the necessary files to the system disk. Then (either as an automated post-install action, or as a separate manual step), those files are used to install the actual working copy of the bootloader into the ESP (or in legacy BIOS systems, embedded into the MBR and the no-man's-land gap between the MBR and the first partition).
When you removed your Mint installation, only the first part was destroyed along with the Mint system partition. But because the ESP is designed to be shared betweeen any and all installed OSs, and you clearly did not damage your Windows installation in the process, you did not remove the ESP. So the old copy of rEFInd and its configuration were preserved on the ESP, in the EFI\refind\ directory where the Mint had originally installed it.
Often, the ESP will be mounted as /boot/efi in Linux, but this may vary between distributions. And if you have multiple disks with an ESP on each disk, or even multiple ESPs on the same disk, the installer may have become confused.
Assuming that the ESP that is being used at boot initially (and contains the "new" rEFInd) is the same as the ESP mounted to /boot/efi on Pop_OS, you should find the "old" rEFInd at /boot/efi/EFI/refind/refind_x64.efi as viewed from Pop_OS. The location of the "new" rEFInd should also be apparent after seeing the sudo efibootmgr -v output.
Note that the "old" rEFInd says:
Boot EFI\refind\refind_x64.efi from 798 MiB FAT volume
and not ... from EFI system partition. That suggests you may now have two ESPs on your system, and probably only one of them will be automatically mounted in Linux.
Also, note that the UEFI bootloader for Windows has the UEFI boot variable pathname of EFI\Microsoft\Boot\bootmgfw.efi. So if the ESP that is currently mounted at /boot/efi is the one that also contains the Windows bootloader, you should find it at /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi. If it's not there, it's probably on the "other ESP" on your system. You don't want to delete the Windows bootloader directory: it contains some files with information specific to your Windows installation, and the only easy way to recreate it is to use the "Repair boot" functionality on the Windows installation media.
