My Internet access provider changes my IP address regularly. Will the website that I will deploy on IIS remain available for external users, even if my IP address won't always be the same?
Talk to your ISP and get a cost for a single static IPv4 address.
Depending on their policies, you might be required to move to a "business" grade connection which will cost more but give you a better SLA, and maybe a small routed block of static IPs.
This becomes a cost/benefit proposition if you're serving a home or business website.
Aside - its worth asking about IPv6 support too. You would like at least a /64 fixed prefix, and a /60 would give you 16 blocks of 4 billion addresses
One method which does not rely on DDNS is implemented by (for example) ngrok, Serveo, and Pagekite. They essentially perform port forwarding over a tunnel to allow users to hit one of their public addresses and get redirected to your private server. It's like this:
[U] is your computer at home. It connects to ngrok and leaves that connection up and running. That connection is a tunnel, which allows network traffic to be passed back and forth . Your Users, then, connect to a public address that ngrok has assigned to you. When they do so, ngrok says "Oh! This traffic is for U!" and it routes that traffic over your tunnel, and your PC sends back its response via the tunnel, etc. etc. ngrok is a little bit like a reverse proxy, a little bit like a VPN, a little bit like a router.
Since the role your computer at home plays is purely as a client in this scenario, it doesn't run afoul of the various inconveniences your ISP will scatter in your path. Worst case they might kill long-lived connections, but the client on your machine will notice and spin another connection up.
I'm surprised Serveo is the only service being flagged. It turns out that many people who manage and secure networks frown upon you opening up your work PC to the Internet, bypassing all the expensive firewalls and IDS and DLP controls they put in place. (I know that doesn't apply to what you do with your PC at home. But if you're wondering who would find these programs malicious, the answer is, any corporate IT team.)