Node-Red is probably your best bet
it's functional with a lot of plugins available as well as relatively easy due to the "flow" workflow

one other command mentioned Home Assistant but even among the Home Assistant community there are quite some people using Node-Red together with Home Assistant to achieve their goals

I use n8n, it has node-based workflows with tons of integrations and even the ability to run Javascript for advanced data processing or logic. You can go way further than IFTTT or even Zapier.

The cloud-hosted version is expensive but it's easy to self-host (self-hosting is free).

https://automatisch.io/

https://github.com/huginn/huginn

https://www.activepieces.com/

Are a few that I saw on the Awesome Self-hosted list

What are you using IFTTT for?

I found that IFTTT has integrations for hardware and software that doesn't always have a clear public API that can replace it. I would like to be proved wrong on this because I'm definitely using IFTTT and would love to replace it. But it's pretty useful still.

What are you looking to automate? Home Assistant does a lot of things that could have been done with IFTTT.

I use huginn. Takes some work to get it setup and do what you want. But its completely selfhosted and really powerful and simpler than writing your own one off ad-hoc scripts. Ask me how I know that...

https://www.openhab.org

Honestly I do all my IoT stuff in plain code, it's actually simpler IMO than trying to use a graphical functional block type interface like NodeRed. And it's a good way for you to get into coding in a way that you can work with real systems in a fairly safe way.

Check out Python's MQTT library, you can build an event driven MQTT handler pretty easily. You set a list of topics you want to subscribe to and then when a message arrives it will call the message handling function. You can check the topic/payload and act on it as you want, publish other messages or perform other operations.

I like distributed control systems myself where individual nodes subscribe to each other and communicate directly (through the MQTT broker) when possible, plus a couple Python scripts running on the broker system to coordinate operations that can't be easily managed that way.

For example an "sundown" topic can be published by a light sensor in the evening, and then either individual lights can subscribe to it and respond, or a script subscribes and iterates through a list of all the lights that are supposed to be on and sends them a power on command. The first option works with custom built endpoints, the second works to integrate Tasmota or similar where several different node devices may exist with different command schema.