Adding my 2 cents
I have done some in house and a LOT of agency work
In house is definitely ‘less challenging’ in terms of not hopping around different tech from project to project, with more flexible deadlines.
In house was a large bank so was more relaxed
All agency work were small businesses
First was terrible company who had no social skills. People used to pop into the office and say good morning, have a nice evening, and that’s it lol. They had unrealistic expectations for a junior dev to get things done
I left but learnt a LOT in a short timeframe but was VERY stressful
Then moved to current role for 3 years - again agency but had more common sense with realistic expectations. The first year was difficult as heck being fast paced.
But personally, I learnt a LOT faster with agency work but that said, the issue with so many projects etc, is that best practise is skipped and this could hamper progression from that viewpoint
The stress isn’t there anymore but at times like all decent jobs there are moments of cluelessness.
Like the first response, no job is safe, there are pros and cons to both choices on in house or agency
What I’d suggest is having a best matchup as possible tech stack wise and tailoring yourself to fit what’s needed. There were always be a big transition period before comfortable so the idea is to prepare as much as possible
Also, never forget to check reviews for any company you apply for - doesn’t matter how much potential a junior has if the company you get into is a mess. One wrong step into the wrong place can hamper your view on the field completely