The latest beta is mIRC v7.57.1965 and can be downloaded here. It includes the following changes:

Beta v7.57.1965 changes:
1.Item 30, added.
2.Item 31, changed. Previous implementation did not allow window names
that contained . periods. Change should be backwards compatible.
3.Item 21, made a few more changes. Now has a 30 second time-out and
handles other issues.
4.Item 32, updated.

Beta v7.57.1701 changes:
1.Item 18, fixed.
2.Item 20, fixed.
3.Item 21, fixed. Note that this change may mean that $url no longer
works with older browsers.
4.Item 22,
5.Item 23,
This means that features that previously required &binvar names
of two letters or more in length now allow just &.
6.Item 16 and 19. Re-ran CppCheck. The main issue with static code
analyzers is the large number of false positives. Each warning needed
to be checked to determine whether there really was an issue. In most
cases, there was not. Issues were found relating to portability,
optimizations, dereferences, pointer arithmetic, sprintf() parameters,
32bit/64bit variables, and so on. Changes were made to 140+ files.

Also installed Visual Studio 2019. For now, it is only being used for
testing purposes, not for compiling the beta or release version. Required
a number of code changes to make mIRC compile.

Beta v7.57.965 changes:
1.Item 11, another partial rewrite of the code used by /run, /exit -nr,
/url, etc. Note that /run may or may not report an error if a file
cannot be run, depending on the version of Windows. Also, /url now
uses a simpler method of opening the default browser.
2.Item 17,

Beta v7.57.669 changes:
1.Item 11,
Partial rewrite of code that affects /run, /url, /exit -nr, opening
DCC Files received folder, etc. The /exit -nr command needs to call
ShellExecute() synchronously, the opposite of other commands which
were fixed for
2.Item 12, added.
3.Item 13, fixed.
4.Item 14, fixed.
5.Item 15, fixed.
6.Item 16, performed CppCheck on the source code.

Several issues were fixed, though most were mitigated in other ways so
were unlikely to cause issues, and others required specific, unlikely
contexts to be triggered.

A large number of 32/64bit portability issues identified which will
need to be changed over time for 64bit version.

Beta v7.57.528 changes:
1.Item 1,
2.Item 2, changed.
3.Item 3,
4.Item 4,
5.Item 5,
6.Item 6,
7.Item 7, optimized.
8.Item 8, fixed.
9.Item 9, added. A large amount of DPI-related code has been added,
including detecting DPIs on different monitors for different windows
and on different versions of Windows, detecting DPI changes for top
level windows, scaling/resetting fonts to match DPI changes, changes
to dialog tabs to handle different size fonts, and so on.

However, most of the code is currently disabled as more work is
needed. mIRC uses a number of DPI APIs, some of which are only
available in the latest update to Windows 10.

10.Item 10, fixed. If files are present, such as with a new install,
they are used. If no files are present, the internal defaults point
to $mircdir. This is partly necessary for backwards compatibility
but the method has been improved.

1.Fixed $+ not correctly reporting string too long errors.
2.Changed installer setting to make it DPI aware.
3.Changed $findfile() to preserve multiple spaces inside a wildcard
4.Fixed /reload interacting incorrectly with Script Editor when a new,
unedited file is created.
5.Fixed $parms returning incorrect values in some contexts.
6.Fixed DCC trust user list bug that prevented autoget from working
correctly for trusted users.
7.Optimized SendMessage() processing to use less memory.
8.Fixed SendMessage() gpf bug where recursive calls result in a stack
9.Updated several features to be DPI aware.
10.Fixed incorrect default location for alias, popup, and remote
scripts when no files are present.
11.Fixed /exit -nr not restarting mIRC.
12.Added /run -a switch to request running as administrator.
13.Fixed script editor bug that was wrapping excessively long lines,
resulting in script errors, instead of truncating them.
14.Fixed SendMesage() handling of negative indexes.
15.Fixed richedit control handling bug that may have caused some
editbox-related code to behave incorrectly if the richedit control
failed to load.
16.Fixed a number of issues identfied by CppCheck relating to range
checking, memory initializations, optimizations, portability, and
pointer dereferences.
17.Fixed script #group parsing bug for invalid group definitions.
18.Fixed $decode() gpf buf.
19.Updated more routines to use 32/64-bit compatible types as step in
preparing for a 64bit version of mIRC.
20.Fixed text file writing bug that could have caused the UTF-8 BOM to
be set incorrectly.
21.Fixed $url not working with newer versions of Chrome.
22.Changed /msg to no longer check for channel/nick prefixes due to some
networks using identical prefixes for both.
23.Changed all &binvar supporting features to allow single character &
as a binvar name for consistency.
24.Fixed $findfile() not freeing handles in some contexts. This also
affected other features that retrieve file lists.
25.Fixed /ignore/protect/aop/avoice gpf bugs.
26.Fixed 64bit time calculations in several features.
27.Fixed memory HDC allocation error check in line marker.
28.Fixed $did().csel potential gpf bug when freeing memory.
29.Changed compiler settings to disable string pooling and enable whole
program optimization.
30.Added /logview -nN switch to scroll view to line number.
31.Changed /play to improve handling of window/file names.
32.Updated OpenSSL library to v1.1.1d.