Have I been hacked?

I have a few computers at home on a small home network. I built a media server pc.
Its an Intel i5-4440 with 16gb of ram and 0.5TB SSD and a couple of 1TB HDD’s for media storage.
Windows 10 home version 21H2, build 19044.1706.
It’s running Plex version 4.76.1.
I don’t have a third party AV program, I am just using the built in windows AV stuff.
For the most part everything is fine and everything functions as I would expect it to.
Lately though, about every other time I wake up the Plex server I get this message on the screen.



How do I want to open this file? It’s an empty file called my.txt. It doesn’t seem to be affecting anything, but it is making me a little bit nervous.
I bought a NAS about 6 months ago, an Asustor AS1102T and I had Plex running on the NAS when it got hacked by Deadbolt. I cleaned it up, got rid of deadbolt and recovered my files. They were basically backups and I had an external HDD for the Plex media. I isolated my NAS from the internet now and I am making daily backups again, but I missed Plex so that’s why I built a home media server PC. But now my Plex server is exposed to the internet.

What should I do?

Any help and or reassurance will be GREATLY appreciated.
TIA

Thanks guys.
I can open other txt files no problem.
And when I try to open this file, it does not exist so I created my.txt so at least I can click on something. But it is empty.
If I delete my.txt then I still get this random message but when I click on notepad it can't find the file.
It's getting annoying.

Thank you everybody.
I scanned my pc with malwarebytes and eset and I think I'm ok.
I re-associated txt files with notepad.
I deleted my.txt
I haven't run chkdsk yet but I will.
I guess I am a little paranoid with everything thats going on in the world and it trickled down.
Thank you again everyone.
I love this board.

possibly just re-associating txt files with notepad.
The other things I tried were just scans
That was really the only thing I did.
I haven't seen the popup in over 12 hours now
sorry if I was overly paranoid but better safe than sorry I guess

- - - Updated - - -

the popup came back but at least I'm not worried about it now.
Like you said its probably a leftover from something I installed, not the Russians or the Chinese trying to break in, not that I'm paranoid or anything.
I was setting up my shop and installing some cameras and some of my industrial neighbors stopped by and saw what I was doing and looked around and asked why? haha I was like one mans junk yada yada Well apparently the same thing applies to my home network. I'm so paranoid about somebody breaking in but why? Why would anybody even want to? I haven't got anything worth stealing haha.