LibreOffice 7.4. was released in August 2022. Can you try a newer version, maybe 24.8 that was released 2 months ago? It is about 2 years of development. Meanwhile, maybe your problem is solved.

I installed 24.8.2.1 via flatpak.
Same issue. LibreOffice Impress does not recognize the second monitor. I can drag the Presenter console to the second monitor. When I exchange, the screens do swap, but Presentation display stays the same size as the original monitor, does not fill the new screen size.

I also notice in my terminal window on the Rasp-Pi where I launched LibreOffice:
 Failed to open display
 libpng warning: iCCP: CRC error
 libpng error: Error reading

I found this in
https://opengrok.libreoffice.org/xref/core/vcl/source/filter/png/PngImageReader.cxx?r=92067587#44

void lclReadStream(png_structp pPng, png_bytep pOutBytes, png_size_t nBytesToRead)
31  {
32      png_voidp pIO = png_get_io_ptr(pPng);
33  
34      if (pIO == nullptr)
35          return;
36  
37      SvStream* pStream = static_cast<SvStream*>(pIO);
38  
39      sal_Size nBytesRead = pStream->ReadBytes(pOutBytes, nBytesToRead);
40  
41      if (nBytesRead != nBytesToRead)
42      {
43          if (!nBytesRead)
44              png_error(pPng, "Error reading");
45          else
46          {
47              // Make sure to not reuse old data (could cause infinite loop).
48              memset(pOutBytes + nBytesRead, 0, nBytesToRead - nBytesRead);
49              png_warning(pPng, "Short read");
50          }
51      }
52  }

I can reproduce this issue with the following configuration:

Version: 25.2.6.2 (x86_64) / LibreOffice Community
Build ID: 520 (Build 2)
CPU threads: 8
OS: Linux 6.14
UI render: Default
VCL: GTK3
Locale: TR (en_US.UTF-8)
UI: EN
Ubuntu package version: 4:25.2.6~rc2-0ubuntu0.24.04.1~lo1
Calc: threaded

I have a HDMI to VGA adapter.

I use an external screen or projector via my computer's HDMI port with integrated Intel graphics. The same issue occurs with both.

I use the GNOME desktop on Wayland. In my computer's multi display screen settings, the 'Join Displays' option is selected. 

My Slide Show Settings show these options under the 'Display' section:
- Auto External (Display 2).
Display 1
Display 2 (External).
- All Displays

Without any configuration:
- The presenter screen starts on the external screen.
- Presentation starting on my notebook screen.
I expected the opposite. 

When I select the 'Display 1' option in the Slide Show Settings, only the presenter screen is shown on my notebook screen. If i hit the overview button, i can see the presentation screen under the persenter screen.

I can also move the presentation screen to the desktop by dragging it with the mouse, in the same way as @badlyshot.

Additional System Information:
00:02.0 VGA compatible controller [0300]: Intel Corporation WhiskeyLake-U GT2 [UHD Graphics 620] [8086:3ea0] (rev 02)
	DeviceName: Onboard - Video
	Subsystem: Tongfang Hongkong Limited WhiskeyLake-U GT2 [UHD Graphics 620] [1d05:1060]
	Kernel driver in use: i915
--
01:00.0 3D controller [0302]: NVIDIA Corporation GP108M [GeForce MX250] [10de:1d13] (rev a1)
	Subsystem: Tongfang Hongkong Limited GP108M [GeForce MX250] [1d05:1060]
	Kernel modules: nvidiafb, nouveau, nvidia_drm, nvidia
02:00.0 Non-Volatile memory controller [0108]: Intel Corporation SSD DC P4101/Pro 7600p/760p/E 6100p Series [8086:f1a6] (rev 03)

~$ sudo hwinfo --monitor
27: None 00.0: 10002 LCD Monitor                                
  [Created at monitor.125]
  Unique ID: rdCR.Ej86D6bHqQ1
  Parent ID: _Znp.NkUqak_Ast4
  Hardware Class: monitor
  Model: "LG ELECTRONICS LG FULL HD"
  Vendor: GSM "LG ELECTRONICS"
  Device: eisa 0x5ab9 "LG FULL HD"
  Serial ID: "512NTTQDT729"
  Resolution: 720x400@70Hz
  Resolution: 640x480@60Hz
  Resolution: 640x480@75Hz
  Resolution: 800x600@60Hz
  Resolution: 800x600@75Hz
  Resolution: 1024x768@60Hz
  Resolution: 1024x768@75Hz
  Resolution: 1280x1024@75Hz
  Resolution: 1152x864@75Hz
  Resolution: 1280x1024@60Hz
  Resolution: 1920x1080@60Hz
  Size: 480x270 mm
  Year of Manufacture: 2015
  Week of Manufacture: 12
  Detailed Timings #0:
     Resolution: 1920x1080
     Horizontal: 1920 2008 2052 2200 (+88 +132 +280) +hsync
       Vertical: 1080 1084 1089 1125 (+4 +9 +45) +vsync
    Frequencies: 148.50 MHz, 67.50 kHz, 60.00 Hz
  Driver Info #0:
    Max. Resolution: 1920x1080
    Vert. Sync Range: 56-75 Hz
    Hor. Sync Range: 30-83 kHz
    Bandwidth: 148 MHz
  Config Status: cfg=new, avail=yes, need=no, active=unknown
  Attached to: #24 (VGA compatible controller)

28: None 01.0: 10002 LCD Monitor
  [Created at monitor.125]
  Unique ID: wkFv.DUuazATfN8F
  Parent ID: _Znp.NkUqak_Ast4
  Hardware Class: monitor
  Model: "BOE CQ LCD Monitor"
  Vendor: BOE "BOE CQ"
  Device: eisa 0x06f2 
  Serial ID: "0"
  Resolution: 1920x1080@60Hz
  Size: 309x173 mm
  Year of Manufacture: 2016
  Week of Manufacture: 32
  Detailed Timings #0:
     Resolution: 1920x1080
     Horizontal: 1920 1968 2000 2142 (+48 +80 +222) -hsync
       Vertical: 1080 1083 1089 1100 (+3 +9 +20) +vsync
    Frequencies: 141.40 MHz, 66.01 kHz, 60.01 Hz
  Config Status: cfg=new, avail=yes, need=no, active=unknown
  Attached to: #24 (VGA compatible controller)