Thanks for your reply. I spend some time with the content of my document to cool my head down. Finally I went for a cheap work-around:

I pasted the same headings with my preferred formatting on Master Sheets, then formatted the page headings on the doc how I want them

to appear in the TOC and made them transparent finally. — Not really cool but a least effective.

Thank you very much. I had read the first link earlier which had then confirmed InDesign`s reading direction. May layout was a little more tricky but I manipulated the frames successfully

As to the second link`s topic; I have used a suggestion I found on https://forums.adobe.com/thread/688971 . I created a character style with No Break tick-marked, applied it to second parts of longer headings and placed a Discretionary Line Break before. Now it automatically breaks down at the Discretionary Line Break (and not before) when the title gets too long for the TOC.

Then finally, thank you for the Auto-Reflowing technique; I have a bigger problem however with another aspect. I want to create a TOC for the
Images, but of course InDesign’s reading direction works against my left-to-right pic numbering. As an example: With three pics each in three rows it would read 1-4-7, 2-5-8, 3-6-9. I had hoped it could read the consecutive numbering of the caption’s paragraph style alphabetically, but it does not. Now applying manual numbers works well with alphabetic reading in the TOC, but it gives a hard time when pictures need to be added later…

Do I miss the forest for the trees ? I you or anyone else could help me with that, this will be a life-time lesson to set up consecutively numbered captions for picture inventories.

Many thanks!

Thank you so much, Mr. Blatner! That was so easy, making me look like a real dumbo : )
Works perfect. – Now please let me proceed to the real problem with this TOC:

Every page has around 8 pics and a separate page heading. I would have liked to include
those headings intersecting the consecutive numbered picture labels in the TOC.
The problem is that InDesign reads from bottom to top. (The labels are read alphabetically.)
So, it comes like this, with the headings right in between:

01 Painter: unknow1
…Source: RoyalArk.net

02 Painter: unknown4
…Tripura State Museum

03 Painter: unknown6
…Tripura State Museum

ROYAL PORTRAITS: 8

HH LATE BIR CHANDRA KISHORE DEB BARMAN 8

04 Painter: unknown2
…Tripura State Museum

05 Painter: unknown3
…Ujjayanta Palace

I read about this as much as I found and I am afraid there is no real solution to it …
hoping you or someone else might come up with a suggestion. Many thanks in advance!