Seguint la moda, m'he instal·lat una instància de Mastodon, però com que faig servir apache per a tot, no volia instal·lar nginx. Buscant per internet m'ha costat trobar una configuració del site d'apache per a que funcionés el mastodon. Com que al final la he trobat, la deixo aquí apuntada, per a tenir-ho de referència i per si pot servir a algú.

    <VirtualHost *:443>

     ServerName **nom-del-servidor**
     ServerAdmin **mail@del.admin**

     DocumentRoot /home/mastodon/live/public/
     <Directory "/home/mastodon/live/public">
             Options Indexes MultiViews FollowSymLinks
             AllowOverride None
             Require all granted
     </Directory>

     <IfModule mod_headers.c>
             Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"
             Header always set Referrer-Policy "strict-origin-when-cross-origin"   
     </IfModule>  

     <LocationMatch "^/(assets|avatars|emoji|headers|packs|sounds|system)">
             Header always set Cache-Control "public, max-age=31536000, immutable"
             Require all granted
     </LocationMatch>

     SSLEngine on
     SSLProtocol -all +TLSv1.2
     SSLHonorCipherOrder on
     SSLCipherSuite EECDH+AESGCM:AES256+EECDH:AES128+EECDH
     SSLProxyEngine On 

     RequestHeader set X-Forwarded-Proto "https"

     ProxyPreserveHost On

     ProxyPass /robots.txt !
     ProxyPass /500.html !
     ProxyPass /sw.js !

     ProxyPass /manifest.json !
     ProxyPass /browserconfig.xml !
     ProxyPass /mask-icon.svg !
     ProxyPassMatch ^(/.*\.(png|ico)$) !
     ProxyPassMatch ^/(assets|avatars|emoji|headers|packs|sounds|system|.well-known/acme-challenge) !

     # these lines don't let webfinger to work properly! 
     # users of other instances will not be able to follow you 
     #ProxyPass /.well-known/ https://**nom-del-servidor**/webfinger/.well-known/
     #ProxyPassReverse /.well-known/ https://**nom-del-servidor**/webfinger/.well-known/  

     ProxyPass /api/v1/streaming http://localhost:4000/
     ProxyPassReverse /api/v1/streaming http://localhost:4000/

     ProxyPass / http://localhost:3000/
     ProxyPassReverse / http://localhost:3000/

     ErrorDocument 500 /500.html
     ErrorDocument 501 /500.html
     ErrorDocument 502 /500.html
     ErrorDocument 503 /500.html
     ErrorDocument 504 /500.html

     ErrorLog ${APACHE_LOG_DIR}/mastodon-error.log
     CustomLog ${APACHE_LOG_DIR}/mastodon-access.log combined

     RewriteEngine on

     SSLCertificateFile **ruta_del/cert.pem**
 SSLCertificateKeyFile **ruta_del/privkey.pem**
 SSLCertificateChainFile **ruta_del/chain.pem**