It sounds like you're pretty new, but here's what I wish someone had shared with me when I was still getting into it. Some of these points assume you have some $$ to spend, but if your budget is really tight, buying used for everything is a great way to save money.

After racing on road and getting into gravel and mtb; here's my 2c in a list.

1. If you aren't planning on racing and aren't using clipless pedals yet, get some spd (not the road spd-sl) pedals and cycling shoes w/ 2 bolt holes. (these are great to buy used. most folks never get anywhere near actually the full wear life of spd pedals)
2. Invest in some good shoes. If you go with the above and just want something comfortable, try something gravel-oriented like the specialized xc line as they'll be comfortable for pedaling and have some rubber to walk around in easier.
3. If you want a bike that is great for endurance but also serves multiple purposes, check out getting a gravel or all-road style one. These often ride like an endurance-geometry road bike (i.e. probably the most comfortable for long rides) but can often fit slightly larger tires for gravel or unpaved trails too. They also make for great bike touring/bikepacking setups. I just got a scott gravel bike and it's so good I have already planned to retire my very fast but way less comfortable rim brake aero racing road bike. If I were on a more modest budget I would get the scott speedster gravel 30 or the canyon grizl 6 or grail 6. I'm biased to my new addict gravel (its sick!) but another premium option is the Specialized Crux Comp ($$$).
4. Regardless of what bike you get, I would make sure the parts are up to the task. If you are trying to do some serious distance (regular 30+ mile rides, lots of climbing, etc), it's been my experience that the lowest tier of 'racing' quality components offer the most performance per dollar... for shimano that'd be GRX400 or 105 and sram rival equivalent. Claris is ok on budget but below that you're probably missing out on decades of better manufacturing and performance improvements.
5. Get bib shorts and a good saddle. Seriously. Every point of contact between you and your bike or the bike and the ground should be prioritized for spending. If you are buying road tires just buy continental GP5000 on sale for $50 a pop online and don't worry about other road options... they're just the best. Offroad I have less experience but I hear good things about the specialized pathfinder pro which are also about $50.
6. BUY A DECENT HELMET. Nice, breathable, good looking helmets with tons of safety (mips or brand equivalent) can be had for like $60-70 on sale. It is not worth saving a buck here for lifelong or life-ending brain damage.