Reproduced against rocky. The same error occurs with two files of 64k size, so the limit seems to be the total request, not the file.

https://dev:8774 "POST /v2.1/2708f8eb31ef4ac89b47f17ccd05d643/servers HTTP/1.1" 413 131
RESP: [413] Content-Length: 131 Content-Type: application/json Date: Mon, 25 Nov 2019 15:11:30 GMT Server: Apache Via: 1.1 controller-node12.dev:8774 X-Content-Type-Options: nosniff x-compute-requ
est-id: req-b245cf71-225a-47b4-b94a-3c9b5dc86588 x-openstack-request-id: req-b245cf71-225a-47b4-b94a-3c9b5dc86588
RESP BODY: {"message": "Request is too large.<br /><br />\n\n\n", "code": "413 Request Entity Too Large", "title": "Request Entity Too Large"}
POST call to compute for https://dev:8774/v2.1/2708f8eb31ef4ac89b47f17ccd05d643/servers used request id req-b245cf71-225a-47b4-b94a-3c9b5dc86588
Request is too large.<br /><br />                                                                         
                                                                                                          
                                                                                                          
 (HTTP 413) (Request-ID: req-b245cf71-225a-47b4-b94a-3c9b5dc86588)
Traceback (most recent call last):
  File "/usr/lib64/python3.6/site-packages/cliff/app.py", line 399, in run_subcommand
    result = cmd.run(parsed_args)                  
  File "/usr/lib64/python3.6/site-packages/osc_lib/command/command.py", line 41, in run
    return super(Command, self).run(parsed_args)
  File "/usr/lib64/python3.6/site-packages/cliff/display.py", line 116, in run           
    column_names, data = self.take_action(parsed_args)          
  File "/usr/lib64/python3.6/site-packages/openstackclient/compute/v2/server.py", line 917, in take_action                                                                                                          
    server = compute_client.servers.create(*boot_args, **boot_kwargs)                                                                                                                                               
  File "/usr/lib64/python3.6/site-packages/novaclient/v2/servers.py", line 1373, in create                                                                                                                          
    return self._boot(response_key, *boot_args, **boot_kwargs)                                                                                                                                                      
  File "/usr/lib64/python3.6/site-packages/novaclient/v2/servers.py", line 810, in _boot                                                                                                                            
    return_raw=return_raw, **kwargs)                                                                                                                                                                                
  File "/usr/lib64/python3.6/site-packages/novaclient/base.py", line 364, in _create                                                                                                                                
    resp, body = self.api.client.post(url, body=body)                                                                                                                                                               
  File "/usr/lib64/python3.6/site-packages/keystoneauth1/adapter.py", line 381, in post                                                                                                                             
    return self.request(url, 'POST', **kwargs)                                                                                                                                                                      
  File "/usr/lib64/python3.6/site-packages/novaclient/client.py", line 78, in request                     
    raise exceptions.from_response(resp, body, url, method)                                            
novaclient.exceptions.OverLimit: Request is too large.<br /><br />

No error found in the nova log, might happen in the wsgi/apache layers?