i think they are but what are the main differences?

They are very similar. I like the OA better. The rocksteady is fantastic.
I also like that the OA has two screens front and back.

I have both , Main difference for Me is the two Screens ... Cant remember the last time I used the GoPro since Buying the Action

Hero 8 has issues, each camera differs, Hypersmooth 2.0 is awesome On, high and Boost, FOV  linear, wide and super-view, Slow mo with  Hypersmooth 2.0.  Livestream in HD1080P. to namea few.  Love theOA for the Front screen  slimmer External mic adapter, and Larger rear display to name a few.  Each camera does things a lil different then the other.   want a trouble free camera stick with DJI.  I say.

I have both too and i'm not already sure of wich one keep.
If we watch the HW part the Osmo win with no problem: Double screen, big size rear screen, better touch, cover lens user changeable, separate door for battery and connection/SD, 3 button and also the possibility to record and charge the battery at the same time. GoPro has the advantage of the hook mounted directly on the cam.
If we watch the SW part the GoPro win: Hypersmooth 2.0, more FOV, Hyperlapse 2.0, flight mode, sharpness control, night foto mode. Osmo has some highlits also here but less noticeable: direct connect to PC (like an SD reader and not like the MTP protocol that use GoPro) a better UI with less lag.
In the front of video quality we are more or less at the same level. In the photo stage Osmo has a better Raw file.
If DJI add a few features in the SW i think that the balance needle will goes for the Osmo definitely.

I like  the OA better for certain reasons:

gopro plug in to a charger, takes a good 7 seconds to light up, OA within 2 seconds it is lit up
GoPro has a led record in the rear, OA does not
Gopro does not show battery overlay  while recording, OA does show more  OSD (online screen display)
I like gopro for the Better interface and manual controls over OA that   semi manual.

the list can go on and on  I own both and I have had less issues then you can imagine with the OA, the good thing about gopro is if you wanted to refresh firmware, you can OA you can not.

People with GoPro at a forum complain more and all user isues many issues, OA form here very little issues so little it is the better  forum.  with how gopro   offers their deals they complicate peoples decisions. lol

And by far the best yet DJI has a repair center on here Gopro does not Lol

My gopro has also a problem that seems started from the Hero 5 black.
If i leave the wifi and the bluetooth ON in the GoPro and i restart my phone (with only Bluetooth ON) the GoPro suddently wake up with no reason (before i reinstalled the FW and the app this hapens also during the normal use of the phone)
So it seems that there is always some "circuit" in "listening mode" also if you have turned off the GoPro (and this drain battery).
SOLUTION from GoPro: turn off the wifi and bluetooth in the cam.

Way to many issues to list for GoPro, I'll list the OA.  Battery exhaust random pop up fw 1.4 nd later this occured, no other issue from me

But with the latest FW GoPro make a great jump over.
Possibility to trigger with movement, speed, any time you want, sunset and duskdown precisely with GPS Sync.
Possibility ti sync the time very precise to use it to sync multiple recording from more camera.
Possibility to make a big one file and make a timelapse of 50 day.
Possibility to make the set of setting you want and save it like a QRCode and use it everywhere you need just by frame the QR.

Not specific OP. If you can join this forum you can google comparisons.