Certificate Issue Downloading File from ModDB

I am having problems using the “GOG + Unofficial Patch” installer for Vampire the Masquerade: Bloodlines. I keep getting the following error message:

Started initial process 82 from /usr/bin/bash -c [ "1" = "1" ] && "/home/elzair/.var/app/net.lutris.Lutris/cache/lutris/installer/vampire-the-masquerade-bloodlines/vtmb-update.sh"
Start monitoring process.
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  4857    0  4857    0     0  14629      0 --:--:-- --:--:-- --:--:-- 14629
--2024-06-20 08:51:29--  https://www.moddb.com/downloads/start/255290/all
Resolving www.moddb.com (www.moddb.com)... 172.67.70.78, 104.26.12.171, 104.26.13.171, ...
Connecting to www.moddb.com (www.moddb.com)|172.67.70.78|:443... connected.
ERROR: cannot verify www.moddb.com's certificate, issued by ‘CN=E1,O=Let's Encrypt,C=US’:
  Unable to locally verify the issuer's authority.
To connect to www.moddb.com insecurely, use `--no-check-certificate'.
Downloading  from https://www.moddb.com/
--2024-06-20 08:51:30--  https://www.moddb.com/
Resolving www.moddb.com (www.moddb.com)... 104.26.12.171, 104.26.13.171, 172.67.70.78, ...
Connecting to www.moddb.com (www.moddb.com)|104.26.12.171|:443... connected.
ERROR: cannot verify www.moddb.com's certificate, issued by ‘CN=E1,O=Let's Encrypt,C=US’:
  Unable to locally verify the issuer's authority.
To connect to www.moddb.com insecurely, use `--no-check-certificate'.
Monitored process exited.
Initial process has exited (return code: 1280)

I posted about this issue in a different thread, and @Asaftiifm helpfully suggested that I had an issue with my certificates. However, I downloaded the script and ran it outside of Lutris, and it worked just fine. Here is the log:

 ./vtmb-update.sh 
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  4857    0  4857    0     0  17182      0 --:--:-- --:--:-- --:--:-- 17223
--2024-06-20 08:37:31--  https://www.moddb.com/downloads/start/255290/all
Resolving www.moddb.com (www.moddb.com)... 104.26.12.171, 172.67.70.78, 104.26.13.171, ...
Connecting to www.moddb.com (www.moddb.com)|104.26.12.171|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Saving to: ‘mirrors.txt’

mirrors.txt                             [ <=>                                                               ]   7.95K  --.-KB/s    in 0s      

2024-06-20 08:37:32 (99.6 MB/s) - ‘mirrors.txt’ saved [8139]

Downloading  from https://www.moddb.com/downloads/mirror/255290/122/7c8d83281b36e9be44ffa4995e6c3540
--2024-06-20 08:37:32--  https://www.moddb.com/downloads/mirror/255290/122/7c8d83281b36e9be44ffa4995e6c3540
Resolving www.moddb.com (www.moddb.com)... 172.67.70.78, 104.26.12.171, 104.26.13.171, ...
Connecting to www.moddb.com (www.moddb.com)|172.67.70.78|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://sjc4.dl.dbolical.com/dl/2023/08/10/VTMBup115rc9.9.exe?st=oip9kQX2hEgxcW8BboQrbg==&e=1718890652 [following]
--2024-06-20 08:37:32--  https://sjc4.dl.dbolical.com/dl/2023/08/10/VTMBup115rc9.9.exe?st=oip9kQX2hEgxcW8BboQrbg==&e=1718890652
Resolving sjc4.dl.dbolical.com (sjc4.dl.dbolical.com)... 103.24.123.144, 2406:bd00:de50:55::144
Connecting to sjc4.dl.dbolical.com (sjc4.dl.dbolical.com)|103.24.123.144|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 589238951 (562M) [application/octet-stream]
Saving to: ‘vtmbup.exe’

vtmbup.exe                                    100%[===============================================================================================>] 561.94M  16.0MB/s    in 33s     

2024-06-20 08:38:05 (17.3 MB/s) - ‘vtmbup.exe’ saved [589238951/589238951]

Might there be an issue with the certificates in Flatpak?

Here are the links to the relevant debug information.
Output of lutris -d
lutris-issue-report.json

Update: I just tried installing it using the .deb version instead of the Flatpak version, and it installed fine.