Another option… How about a really long flat cat6 Ethernet cable?

… in 2023 no reason to separate…

Disagree heavily, (In cases when there’s no need for high performance devices to ever consider slower 2.4GHz g/n networks littered with 10year old iot stuff, they’ll still sometimes pick 2.4… and there’s usually no other way to configure this restriction on clients), … but that’s a bit of a longer discussion.

MoCA could be a nice hack if coax is there between floors and Ethernet isn’t.

Also, there’s “fancy” wifi client gear from Mikrotik in 50-100 bucks range, stick one end into Ethernet, point it towards the router and enjoy the +20dB of signal, as if the PC was in the same room.

(I apologize for using Mikrotik and fancy in the same sentence, but compared to most desktop adapters , the CLS of Mikrotik is kind of fancy, … I’m thinking of their sq5 series here in particular)

Too many variables in how WiFi can be set up, hard to tell.

Since you’re in a house, and I’m guessing in the US (mentions of microcenter), try the following:

• Separate 5GHz wifi network from 2.4GHz by giving them separate names.
• Set the channel on 5GHz to 36 or 149, instead of Auto.
• Set the channel on 2.4GHz to 1 or 6.

Then, stick to 5GHz on all devices that support it and where you have a choice, e.g. “forget network” the 2.4. …

… and see how that goes.

If you don’t need wifi, you could get a 1GB ram raspberry pi 4 + TP-Link USB dongle for a second 1GBps interface.

Can you be a bit more specific about what your needs are?