StartPage crashes Safari when opening a new tab

Seems to have happend after updating to MacOS 26.0.1 (25A362), with Safari version 26.0.1 (21622.1.22.11.15)

Changing "New windows open with" and "New tabs open with" to "Empty Page" or "Home Page" pointing to another website works fine. It's specifically when using StartPage.

Repo steps:

1. Fresh startup of my MacBook
2. Open Safari
3. Create a number of tabs (by default opens Startpage) (at this moment it works fine)
4. Close Safari using the red button on the top left of the window
5. Open Safari
   1. A new window is created but is not visible and I cannot get it to show
6. Force quit Safari
7. Open Safari again
8. Creating 1 - 2 tabs causes Safari to crash with the following exception:

Exception Type: EXC_CRASH (SIGABRT) 
Exception Codes: 0x0000000000000000, 0x0000000000000000 
Exception Reason: *** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[2] 
Termination Reason: Namespace SIGNAL, Code 6, Abort trap: 6 Terminating 
Process: Safari [6479]

• This persists until I shutdown and startup my MacBook

What I've tried:

• Disabling extension, I've got only 1 (AdGuard) installed
• Reinstalling MacOs
• Booting in safemode
• Hiding everything on the StartPage
• Clearing cache and website data

Unfortunately non of these fixes worked. I do have iCloud sync enabled, disabling it on its own didn't fix it, but maybe it still syncs some corrupted files, I've got no clue where to find those however.

Can anyone help me out? Thanks in advance!