Alright, so here's the crux of the problem:
Today at the early morning I was playing Gwent just fine like the usual, by using a computer mouse as my default/preferred controlling device of choice. Somewhere around 11:00 (11AM) hours by Moscow time my local ISP had sudden unexpected problems and so my internet connection was completely cut right at the middle of one of the matches (so the game gave me an automatic loss due to timed out loss of connection). I then closed the game due to being unable to play it, for obvious reasons.
Then, since I was completely without any internet connection for several hours, I've decided to play some other game installed on my PC, a game that was 100% offline and didn't connect to anything at all, and it wasn't related to GOG's services/apps or CDPR in any way, shape, or form. To play this said offline game I was using Sony's official DualShock 4 (v2) joypad, which I usually connect via an official wireless USB dongle/adapter made by Sony for the said joypad. So, I've played my offline game for a couple hours just fine, before my ISP sorted out their issues and my internet connection was eventually restored back up at around 13:00 (1PM) by Moscow time. During all this time GOG galaxy and all other GOG/CDPR-related things were completely turned off.
When I got my internet back, I exited my offline game and turned my DualShock 4 completely off. Then I've launched my GOG galaxy client and Gwent back up...and noticed that my mouse doesn't work in the game anymore...and that the game now shows PlayStation's controls' overlay (L1/R1/R2/L2 buttons, cross/circle/triangle/square, the touch bar, and etc), and game itself controls only either from the said joypad, or by a keyboard. MY MOUSE STOPPED WORKING ENTIRELY (I can only move the cursor during the very first loading screen with CDPR's logo bird, then it disappears and my mouse doesn't work anymore from there on), only leaving joypad and the keyboard.
And I can't change this in game's own settings anywhere because there are NO controller type settings to choose from in the game to begin with, AND uninstalling/verifying/repairing game's files does NOTHING at all. I even tried to do everything at the same time (uninstalling, unplugging my wireless dongle, rebooting PC, then installing the game manually back on and verifying/repairing, then rebooting once again) and nothing helped so far. PLEASE someone help me with this. I absolutely cannot play this game with a joypad or ESPECIALLY by using a keyboard, it's an utter torture! I want my mouse controls back! This is clearly a bug of the game, since it applied PlayStation's (Direct Input configuration, I presume) control scheme/overlay while I was NOT enabling that on my own volition in any way, shape or form. I was playing a completely unrelated offline game with my DualShock 4 and during that time all of my GOG/CDPR services were completely turned off, so I sincerely don't know how in the hell this could've happened!
Here's a couple screenshots of how it looks like right now (it, obviously, wasn't like that at all, during this morning):