So I downloaded the latest Ubuntu 25.04 OS ISO on April 17th, the first day available and wrote the ISO file to my flash drive using RUFUS on my windows11 laptop.

I installed it to my working hardware system (see below for specs) after backing up all data and installing with wiping the ssd drive for a fresh install. 

Welcome to Ubuntu 25.04 'Plucky Puffin'
I did a "default" install of 25.04, with these additional options checked:
1) What apps would you like to start with: check "Extended selection"
2) Install recommended proprietary software?: check both "Install third party software for graphics and WiFi hardware" & "Download & install support for additional media formats"

After several days of frustration, I have discovered that remmina ver. 1.4.39 won't run on 25.04, an app I use all the time; I copied over my existing, working under 24.10 remmina connection profiles but they won't work;

Remmina will start up and display "Accept Certificate" screen, and when I click Yes, it displays this message saying:
error:  Could not connect to the RDP server "192.168.3.53" via TLS. See the DEBUG traces from a terminal for more information.

After several days of frustration and so many avenues I went down to try and resolve this issue, what worked for me was to completely uninstall the remmina app on my system and install the flatpak version of remmina (ver 1.4.40); this works normally and as expected.  https://www.remmina.org/how-to-install-remmina/

I'm not sure if there is some problem with the 1.4.39 version; I didn't try specifically testing for this, if 1.4.40 resolved some issue on previous.

Some different things I tried to resolve;
1) install openssh-server on my win11 laptop, the current and only target I use here at home.  After installing openssh-server on both my 25.04 & win11; no joy
2) completely uninstalled remmina and reinstalled (several times); I also installed Ubuntu 24.10 just to check out if my hardware was to blame; but it works as expected on 24.10.
3) so next thing to check; if this remmina a snap install? check /home/dave/snap and see if there is that folder there; NOPE;   how to check if an app package is installed?
$ apt list --installed | grep remmina and this showed that it was probably installed from .deb file;
4) Remove the remmina app completely;   $ sudo apt-get purge --auto-remove remmina
5) tried installing 24.10 and then upgrading to 25.10; NOPE; and remmina would not even start up at all!
6) I tried setting the debug vars G_MESSAGES_PREFIXED=all & G_MESSAGES_DEBUG=all;  and looked at this /tmp/remmina_log_file.log  ;looked at this log file but no obvious error/warn msgs; the extra debugging messages did not give me any clues as to resolve this.
7) Then followed these steps found on this web page:
How to install Remmina  https://www.remmina.org/how-to-install-remmina/
(you first have to install the flatpak app: $sudo apt install flatpak)
--- FLATPAK section ---
After this install, I can search for 'remmina' and it shows up and I can start it up and pin the app icon to the dock; and it works as expected using my previous connection profiles.


Here is my current hardware; probably look to pick up new, updated, latest gen hardware in the near future.
CPU0: 11th Gen Intel(R) Core(TM) i9-11900K @ 3.50GHz (family: 0x6, model: 0xa7, stepping: 0x1
DMI: Gigabyte Technology Co., Ltd. Z590 UD AC/Z590 UD AC, BIOS F2 01/06/2021
2x16gb DDR4 3600 dimms, total of 32gigs ram
2tb NVMe SSD
NVIDIA Corporation GP104 [GeForce GTX 1070] using the nouveau driver;
(I'm not much of a gamer)



Some commands and links I found useful;
apt list --installed |grep remmina

pkill remmina
ps -ef |grep remmina

sudo apt-get purge --auto-remove remmina

sudo find / -name "*remmina*"

How to install Remmina
https://www.remmina.org/how-to-install-remmina/

after upgrade install from 24.10 to 25.04 completed and rebooted, remmina would not startup at all; dead; so completely remove remmina;
https://askubuntu.com/questions/187888/what-is-the-correct-way-to-completely-remove-an-application#187891

google: HOW TO compeletly uninstall remove purge remmina from ubuntu 25.04
and upcomes the AI Overview
To completely uninstall Remmina from Ubuntu 25.04, including its configuration files, use the following command in the terminal:
sudo apt-get purge --auto-remove remmina
Alternative Method (if installed from Snap or Flatpak):
If you installed Remmina using Snap or Flatpak, you'll need to use the appropriate uninstall commands:
    Snap: sudo snap remove remmina.
    Flatpak: flatpak uninstall org.remmina.Remmina.

Important Note:   Using the sudo apt-get purge command will remove not only the application but also its configuration files, ensuring a clean removal. The --auto-remove option will remove any dependent packages that are no longer needed after Remmina is removed.


My Thinking About This Issue, et al:
[I sometimes think I am the only one having these types of issues; for example, I have used ultra-edit text editor for decades, but starting in about 22.04 and on, the clipboard does not work as expected; when I ctrl-v in uex from another source (webpage, article, other text editor) it doesn't paste the text into the uex file; I contacted the vendor but they had not heard of that problem; I have since discovered it appears to be a problem with the Gnome desktop as other desktops do not exhibit this clipboard issue.

And when I first started having this issue with remmina, and searched for the "Could not connect to the RDP server "192.168.3.53" via TLS. See the DEBUG traces ... but I did not find any current posts; all were years old, with similiar wording]