Not quite.
You connect your phone to your PC via USB, boot the phone into Fastboot Mode, and then you execute fastboot boot twrp.img (or whatever the filename is) in a command line on the PC.
This will then boot TWRP on the phone without you having to install it. Nothing will change on the phone, as long as you keep System read-only in TWRP (important!) …
You can then use TWRP on the phone to backup the partitions …
Here’s a little something in case you’re interested …
I’m not sure I would tell this here, if I wouldn’t, please tell me, I’ll delete my message. I’ve encountered a problem rooting my phone using twpr and magisck. May anyone help me ? I’ve created a new post in order to avoid “flooding” this one, here Problem with rooting FP3
And really sorry if my ask seems to you inappropriate.
So, I’m on A0111 and rooted with Magisk. How does the update process look like for me? Can I just flash the A0111 image to restore stock boot, update, and then re-do the Magisk root procedure? Or do I have to be more careful and do something else before?
You should be able to directly do the OTA update. And you can even keep Magisk by just uninstalling it (restoring images, not full uninstall), then install the update normally but DO NOT REBOOT, then on Magisk, select “install in inactive slot (after OTA)”. This should work if you did not modify the system partition (mount read only).
Hey, thank you very much for your response. Sadly, I didn’t keep my system partition read only when rooting, so I guess flashing the stock sytem image is unavoidable for me.