Especially with cable (TV) connections, ISP's can have some issue with a store bought modem/router device, instead of the modem/router device they themselves provide. Frequency ranges not being exactly how they want it or something like that, was the explanation of the tech who installed it at work (only type of connection available at that location).
But with ADSL/VDSL connections (land-line) ISP's don't care. Just fill in the correct values for your store-bought modem/router to communicate with their hardware and you are golden. Have done that myself several times.
Now there is a fiber connection in my home and I have not seen a place yet where I could buy a consumer modem/router for fiber connections here in Paraguay, if the need would arise.
What the previous posters already said. It is very dangerous to connect any computer directly. There are many 'script kiddies' who scour public addresses continuously for any "kink in any armor" and when found, attack it mercilessly until they are through. As Windows is very popular operating system, there are many 'kinks" known and unknown for it that those people will make use of to make your system a bot, fill it with ransomware or virus. Using popular operating systems makes it easier for their nefarious purposes and/or ill gotten gains.
However, if you are hell bent on connecting this way, you better have a spare PC with at least 2 network cards available and install OPNSense or pfSense on that device. Those are software firewalls, running on a hardened version of the FreeBSD operating system. While no operating system is absolutely safe, the BSD operating systems come closer to that goal than other OS's.
Connect your ISP's line directly onto this firewall device and use the second network card to connect to your laptop or switch, if you need more devices connected. This type of firewall is much more competent at warding off attacks than a software firewall on Windows could. Default settings on bot OPNSense and pfSense are already pretty strict, so the don't require much work if your needs are simple.
Still, it is better to wait for a modem/router from your ISP, that is the safer option. But if it is an option and the budget allows for it, pay the full amount for their new device upfront. That monthly paying crap is costing you more on the long term.
ISP's that I have used in the Netherlands and here in Paraguay never charged me for such a "service" of theirs. Whenever I had a broken device of them, it was always exchanged for free. One time because of a lightning strike nearby and another time because I had an old device that wouldn't be able to handle the higher speeds that the ISP was about to offer me.