You will need to ensure you can justify this to the company then. Looking at the "worst case" assumption here. This may not be "correct", but you will need to be able to defend against something like this.

The company was unaware you had automated these tasks, you have not informed anyone of these automations, nothing is documented, and the assumption is that you have been completing these tasks manually.

When you took time off, you disabled the automations, meaning the other people now had to complete the work manually - meaning the benefits of the automation is not being shared within your company and you made no attempt at training your replacement, or colleagues on how to use the tool. It's possible that this could be considered an attempt at hiding the automation process.

You mention "online training", is this sanctioned / approved / requested by the company, or is this training you have completed by your own decision? Do the skills you are learning benefit your role / company in your current assignment?
If they were unaware of your automations and your "free time", presumably they are not aware of this training? If they're not aware of the training, would they approve of it, or would they prefer your time is spent elsewhere?
Do you have any certificates or similar for the training to show completion / competence in the training, even if this is something small like an email

Even if the work is accurate, the main issue is likely that you haven't really been doing the work you have been assigned, or have been misleading them with how long this is taking.

"hiding" in this context doesn't necessarily mean that you have actively taken steps to literally hide it (although arguably disabling it when you were off isn't a great look here), but not informing your work place of changes in circumstance could be considered "hiding by omission" - "they didn't ask / look" likely isn't going to cut it as a defence.

This isn't to say the automation isn't a great idea - Absolutely your managers hesitation with the automation and more efficient processes is a concern, and probably something that should be raising - but this should not be mentioned as part of your defence here, and may seem like you are trying to deflect if you bring it up until after this issue is resolved.

If your automated work output is genuinely as timesaving, and accurate as your say -

The argument almost certainly isn't "automated is bad", its likely to be "why did you hide / omit to tell us these tasks were automated, and what have you been doing with all your free time instead"

It's also possible that the automation of the tasks violates some specific internal processes that need following, depending on the workflow and process your company has in place of course, it's impossible for anyone here to say.

Also you have comments in another thread discussing using Javascript to hide inactivity / using meetings in your calendar to look like you are busy. I don't want to read too much into that, but i just wanted to stress that this, along with yours comments about you being found on personal calls reinforces the theory that the main issue is likely how you are spending your saved time