For documents I just use LibreOffice and suffer; if I absolutely need Office I suppose I could use my old discs and install it on the Windows machine, but have not had any need to in the past 3 years since I switched. When I send documents to people I just export as PDF and they're none the wiser.
Save for extracting BIOS updates from custom .exe files (thanks HP and Dell) I never use either of them.
> Word/Excel documents
I run Office 2010 in Crossover, which works very well. (I have a copy of 2016 as well, but it is slower.) You can also try WPS office, which does a decent job of handling Office documents.
> updating the firmware of IOT things
I have a Windows VM and I use USB passthrough for things like iTunes. I usually use it less than once a month.
Prior to having CrossOver, I used PlayOnLinux. When I last used it, Office 2010 worked, but had some issues such as fonts not being embedded in exported PDF files.
It may also be possible to install Office through Steam, which has the Proton compatibility layer based on Crossover. There is some information on using Proton for non-steam games here: https://streamable.com/pukwz
Of course, Crossover is just an enterprise supported version of Wine, so you could probably get Office working in plain Wine, but the automated setup support a tool like Crossover or PlayOnLinux provides makes it significantly easier to get things working without unusual and difficult to troubleshoot issues.
I don't deal with proprietary IoT things. If I did I probably would KVM it, yeah.
I generally just don't care about things that aren't supported. Probably not the answer you're looking for, but there it is.
I used to deal with a lot of MS Office documents, less so now. Most forms and web docs are PDFs and there's a growing crowd of people happy to send Open formatted docs. I've used Libre/Open Office for about 5 years as my main office suit and had no issues. It does feel less polished, and I do miss the "styles" thing you can do with MS Word but for copy I find it perfectly adequate.
If I need professional typesetting, or really anything more than Libre Office can handle, I use LaTeX. It's actually very quick.
You can also use MS Office online; their web editor is very good. I use it when I need to preserve an MS Word themed document's formatting.
These edge cases (and the uneasy feeling that there are many others that I won't discover until I make the switch) are the main reasons holding me back at the moment. The lack of interoperability because Linux is not an established consumer OS (yet).