Yes, you can run Grin++ in your Raspberry Pi 4. You download the binaries from here. Inside the folder you will find and .AppImage file if you want to run the GUI, but also the node binary compiled for Linux-ARM64. You will probably need to install some libraries to run the AppImage file depending on your installation.
Linux rpi4-20210718 5.10.0-0.bpo.7-arm64 #1 SMP Debian 5.10.40-1~bpo10+1 (2021-06-04) aarch64 GNU/Linux
If you want to compile it from source, you will need to do it on a Pi or using QEMU. Later I will be writing a tutorial from beginning to end on how to do it. The GUI looks nice, but probably using the CLI could be more convenient, contributions are welcome.
Feel free of joining Telegram: Contact @GrinPP.