How to use Cloud sync apps to move desktop folders to cloud?


What I am trying to achieve?
I want to move most of my files that sit on my desktop which are important and used frequently to cloud based sync apps like google drive, iDrive, Box etc. I want to be able to access them seamlessly across my different computers. (I am aware that is what those cloud folders already do)

I have had a weird serial failure of my computing devices, starting with my desktop which had to be shipped so I got it packed, found my laptop with a broken hinge, got it repaired and it was my primary device for a few months, then I got my desktop back but the GPU failed and I got a used one now, in the end I am stuck on whether to use my laptop or desktop now.

Light computer work, a little more advanced than how our parents would use a PC.

My present knowledge about cloud apps:
I have a google drive by default as most people with gmail accounts do. I tried their Backup & Sync app and noticed folder that synced everything in it to the cloud. So I used this to work on my thesis on my desktop which was more comfortable at home and was able to show my progress to my Professor and guide for feedback. I was very happy with this arrangement and the free 15GB remained more than adequate for a couple of years. I then moved my important documents, degrees, certificates, IDs to this folder as a last resort if needed.
I also have iDrive 5TB cloud backup subscription that automatically backs up my entire PC. It too comes with a Sync folder with a 15GB limit.
My present idea is to download all of those sync apps, I have a paid account on Google Drive & iDrive and free ones on Dropbox, Box and another Gmail account and use them as separate folders sitting on my desktop.

So what more do I want:
I just want validation if my plan is good or is there a better way where I can use one app to sync files across different providers. Or better apps to sync than the ones I mentioned above. I am looking for free solutions if possible or paid ones at nominal cost.
Basically if my present Google drive supported 50GB for the sync folder than I would have been content. But so is not the case even for the (100GB) paid account which I have.

What am I not looking for:
I am not looking at backup solutions. I already have a $80 5TB/year subscription for all my important files (mostly photos and videos) including complete HDD clones, paid Gmail account for phone backups and access and 2 different HDDs for redundancy. To top it I have an internal HDD that just sits in my cabinet disconnected if all else fails.
I am not up to date with technology for the past half decade due to my residency and then the prolonged pandemic leaving no free time for hobbies hence a lot of my tech knowledge isn't updated from 2016

My query right now is only for a home user with 2-4 different laptop/Desktop PCs and the quest for uniformity of access to files.
In the future I may have to use a similar system for my clinic and use it to sync medical files and documents seamlessly and safely with highest importance on privacy between my Home PC and Clinic PC. So any advice on slightly expensive alternatives for cloud syncing files is highly appreciated. This will be entire different system of IDs and computers, disconnected to my personal account and not related to the outcome of this thread.